Category: dog

Mitral valve disease

Mitral valve disease is the most common cause of a heart murmur in dogs. Many cases are detected by a vet after a routine examination (such as before vaccination) before dogs show any signs of illness. If your dog has been diagnosed with mitral valve disease your vet will offer advice on when (and whether) treatment is necessary. Many dogs with this condition live long and happy lives.

The dog’s heart, like that of humans, is a muscular pump with four separate chambers. The right side of the heart sends blood to the lungs where it picks up oxygen. The left side of the heart pumps the blood around the body. The four areas of the heart are separated by valves that ensure the blood always flows in the correct direction through the heart. The mitral valve lies between the 2 chambers on the left side of the heart. It prevents blood from flowing backwards (towards the lungs) rather than around the body when the heart contracts.

Damage to the mitral valves can occur in a number of ways. The most common disease is degeneration of the valve as a result of ageing (this is called endocardiosis). In other cases the valves may fail to develop properly, e.g. mitral dysplasia, or can be affected by infections carried in the blood (endocarditis).

Damaged valves do not work properly – abnormal valves allow leakage of blood between the heart chambers. When valves are leaking the abnormal blood flow can be detected when listening to the heart (a murmur).

If the valve is leaking not all the blood leaves the heart with each contraction and so the heart has to beat faster and harder to pump the same amount of blood out into the circulation. The increased work eventually leads to heart failure.

Many dogs with mitral valve disease have no outward signs of illness. The murmur is often detected by a vet after a routine examination (often at a health check at the time of vaccination). Degeneration of the valve is more common in certain breeds of dog, particularly small breeds. In some breeds – notably the Cavalier King Charles Spaniel (CKCS) – dogs often inherit the condition from their parents.

If your dog is from a breed with a high risk of developing mitral valve disease you might ask your vet to check them for the presence of a murmur. Most animals with mitral valve disease are middle-aged or older but young animals can be affected.

The initial sign of mitral valve disease may be reluctance to exercise, or coughing due to heart failure or direct pressure on the large airways by an enlarged heart.

If your vet hears a murmur when listening to your dog’s heart they may want to do some other tests. Murmurs are very common findings and if your pet is well there may be nothing to worry about. However, even if your pet has a problem such as coughing your vet may find that the cough is caused by something else and the disease of the mitral valve is not causing any problems.

X-rays are very important in the diagnosis and monitoring of heart disease. On the X-ray of your dog’s chest your vet will be able to see the size of the heart and also any effects on the lungs and blood vessels. Enlargement of the blood vessels in the lungs or evidence of fluid in the chest may be the first indication of heart failure and, if these changes are present, treatment should be started immediately. One of the important benefits of chest X-rays is that they will help your vet to rule out respiratory disease as a cause of coughing.

Although examination and other tests may make your vet suspect that your dog has heart disease ultrasound is the method of choice for finding the actual cause. With ultrasound you vet will be able to see the heart valves and it may be clear that they are not meeting correctly. With some special ultrasound machines patterns of abnormal blood flow around the valve can be seen. Ultrasound examination of the heart requires considerable knowledge and experience and should always be performed by experts.

Your vet may also want to do some blood tests (particularly to check that their kidneys are working properly) before starting your pet on treatment.

If your dog has damaged heart valves these will not repair. The only permanent solution is to replace the valves. In man, replacement of damaged heart valves is possible and whilst this procedure has been carried out successfully in dogs (usually those born with a malformed valve) it is certainly not considered standard practice in pets. However, since the disease often causes few problems your pet may be able to live quite happily with the disease. If heart failure develops medication can help your pet to lead a happy life.

Many animals with mitral valve disease show no signs of heart disease and these patients require no specific treatment. If your pet is not showing any signs of ill health your vet will just monitor them regularly to detect any progression of disease. If heart failure develops then appropriate treatment can be started.

There are many drugs that can help animals with heart failure and these include:

  • Diuretics (usually furosemide and spironalactone) to stop fluid retention in the circulation and the lungs
  • ACE inhibitors to help to prevent fluid retention and make it easier for the heart to pump blood
  • Pimobendan – to improve efficiency of heart function
  • Digoxin to slow the heart rate and may help it to function more effectively.

Not all these drugs are appropriate in every animal and your vet will decide on the best treatment programme for your pet and will discuss these choices with you. Often a combination of drugs is needed and the doses of drugs may change with time. Usually once treatment has started it will need to be continued for the rest of your pets life.

There is no evidence that it is beneficial to start treatment before signs of heart failure develop in dogs with mitral valve disease.

Many animals with degenerative mitral valve disease live out a normal life span with no signs of heart disease. Some CKCS may develop heart murmurs at only a few years of age but not even all of these will develop clinical signs associated with the condition. Animals with significant heart failure require therapy and the outcome will depend upon how well they respond to this therapy.

Investigating heart disease

It is important that your vet can recognise the early stages of heart failure (and therefore when to begin therapy, if necessary). Investigations of animals with heart disease are important to identify early signs of failure and to establish the appropriate timing and type of therapy. Heart disease and heart failure are not the same thing. In the early stages of heart disease most animals are able to cope although their heart is not working as well as normal. Animals can live with some forms of heart disease without showing any signs of illness at all. Heart failure occurs when the heart disease is more severe and signs of malfunction (usually coughing or breathlessness) develop. Investigations of animals with heart disease are important to identify early signs of failure and to establish the appropriate timing and type of therapy.

When heart function is compromised there are many mechanisms that come into play to reduce the impact on the animal. Since few pets are athletic, heart disease can be present in many without their owner noticing any ill effects. Many cases of heart disease are detected by the vet at routine examination, e.g. before vaccination. Abnormalities are often detected in the first 2 years of life, if congenital lesions are present; or in middle-aged to older pets when acquired degenerative changes develop. Owners generally notice signs once heart failure has developed or if their pet has problems during periods of stress or excitement.

Clinical signs of heart disease vary according to the area of the heart affected. They range from coughing and weight loss to abdominal distension (ascites) or collapse.

Clinical examination

A full clinical examination is essential in all patients with suspected heart disease. Abnormalities in the heart may cause changes to the pulse rate, rhythm or strength. The pulse should be assessed at the same time as listening to the heart to confirm that every heartbeat generates a strong pulse. Poor heart function may also result in congestion of the veins (fluid retention). By listening to your pet’s heart with a stethoscope your vet can determine the rate and rhythm of heartbeats and hear murmurs or other abnormal heart sounds. Ideally blood pressure should be measured in all patients with heart disease.


X-rays are very important in the diagnosis and monitoring of heart disease. Assessment of the heart size and shape itself is important but the lungs and blood vessels visible on the radiograph are also examined. At least two pictures of the chest (one with the animal lying on its side and one lying on its belly) are needed for complete x-ray assessment of the heart. In almost all cases it is safer to administer a low dose of an appropriate sedative than to risk a patient struggling when x-rays are being taken.


Ultrasound is the method of choice for determining the cause of structural heart disease. It allows the vet to see the heart structures, ie myocardial thickness, the relative sizes of the heart chambers, and the position of the valves and major blood vessels. Echocardiography also allows the vet to watch the heart beating. The motion of the valves, contraction of heart walls and abnormal patterns of blood flow can be seen. Echocardiography requires considerable knowledge and experience and should always be performed by experts.

Laboratory tests

Routine laboratory tests (particularly assessment of liver and kidney function) are important for monitoring of animals with heart disease. The dose of many drugs used in the treatment of heart disease may need to be altered in patients with reduced liver or kidney function. It is important to assess kidney function in all patients before they start on long-term therapy for heart failure.

Electrolyte abnormalities are common in patients with heart failure and some drugs can make these imbalances worse. Low potassium levels can develop as a result of inappetence and the use of some diuretics, e.g. furosemide.

There are now some laboratory tests which allow us to measure substances produced by damaged hearts and these tests are likely to become increasingly important in the diagnosis and management of heart disease in the future.


The electrocardiogram (ECG) measures the electrical activity in the heart. Although measurements made on ECG can provide an approximate guide to the size of specific heart chambers, x-ray or ultrasound are better for assessing heart size. The most important use of ECGs is in the monitoring of abnormal heart rhythms (arrhythmia).

High blood pressure (hypertension)

Hypertension (high blood pressure) has long been known to be a problem in people and is being increasingly recognised in pets. Hypertension is very common in older people and is often associated with smoking, or with stressful living. In animals, hypertension is almost always caused by an underlying disease.

When the heart contracts a pulse of blood is forced through the arteries. This pulse generates thesystolicblood pressure. In between the heart contractions the pressure in the arteries falls this is thediastolicblood pressure. In animals we mostly measure systolic blood pressure.

Systolic pressure does not stay the same at all times. Arteries are constantly being constricted (narrowed) or dilated (widened) so that blood can be diverted to whichever organs are most active at the time. A dilated artery has a larger diameter, making it easier for blood to flow through. Less pressure is needed to pump blood through the dilated artery and so blood pressure is lower if arteries are dilated.

Blood pressure also tends to increase a little with age. The arteries of older pets tend not to be as elastic as in younger animals. These arteries do not dilate easily so the overall resistance to blood flow is increased, resulting in higher blood pressure.

Hypertension in animals is almost always secondary to other problems. In dogs the main causes of hypertension are kidney disease and hormonal conditions such as diabetes mellitus and hyperadrenocorticism (Cushings disease).

In hypertension the increased pressure in the blood vessels damages the vessel walls, causing bleeding and blood clot formation. This causes particularly severe problems if blood vessels in the eye, kidney, heart or brain are affected. In addition when blood pressure is high the heart has to pump against a greater resistance and this places increased strain on the heart muscle.

In the early stages of disease there are few, if any, signs of hypertension itself, but because hypertension is commonly associated with an underlying disease you may notice signs of that disease in your pet. Appetite may be decreased in kidney failure, or may be increased in diabetes, and both conditions can cause weight loss, excessive drinking and occasionally vomiting.

Signs related to secondary damage to blood vessels will depend upon the organ affected. Damage to the blood vessels in the eye may cause sudden onset blindness, and this is often the first recognisable indication of hypertension in cats. Damage to blood vessels in the brain can cause strokes and other neurological disorders, and increased blood pressure in the blood vessels that supply the kidney can cause further deterioration in kidney function.

If your vet suspects hypertension they will want to examine your dogs eyes for areas of haemorrhage (bleeding) or detachment of the retina (at the back of the eye). Examination of the eyes can be a very useful way to identify the disease but the best way to confirm the diagnosis, and to monitor the response to any treatment, is by measurement of blood pressure.

Measurement of blood pressure is becoming more common in veterinary practice although it is not yet part of the routine examination in most cases.

The method used to measure blood pressure is very similar to that used routinely in people, but because of the small size of the arteries more specialised equipment is needed. An inflatable cuff is placed around one of the dog’s legs (or sometimes round its tail) and the vet uses a small receiver held against the arteries in the foot (or tail) to detect the pulse. The cuff is then inflated and deflated a number of times and the vet listens for changes in the sound of the pulse as the pressure in the cuff increases and decreases.

The process only takes a few minutes; does not hurt and most animals do not object at all. Blood pressure needs to be monitored regularly in animals that have been diagnosed with hypertension and most pets soon become used to the procedure.

Most healthy dogs have a systolic blood pressure of between 120 and 180 mmHg. A dog with a blood pressure that is consistently over 180 – 190 mmHg is considered to be hypertensive, although older animals do tend to have slightly higher blood pressure than young dogs. Sight hounds, e.g. Greyhounds and overweight dogs tend to have higher blood pressure.

If an underlying cause of hypertension can be identified this disease should be treated, and if the blood pressure is only slightly elevated then this may be sufficient to bring blood pressure down into the normal range. However in most cases it will be necessary to use additional treatments which are specifically aimed at lowering the blood pressure.

For long-term management of hypertension in dogs ACE-inhibitors e.g. enalopril or benazapril may be used, but if these are not producing enough effect other drugs may be added. Other groups of drugs which may be effective include calcium-channel blockers and beta-blockers. Animals with hypertension have individual responses to treatment and it is important to monitor the blood pressure closely once treatment has been started, altering the dose of the drugs, or altering the medication as necessary. In patients with kidney failure, it is also important to monitor kidney function when using anti-hypertensive drugs.

Feeding a low salt diet may also be of value, although it is unlikely to be sufficient as a sole treatment of hypertension. You should avoid feeding pet treats to dogs with high blood pressure since most of these are quite high in salt. Most hypertensive dogs can be fed a normal commercial dog food, although your vet may recommend the use of a prescription diet for management of underlying disease, e.g. chronic kidney failure.

If your dog has suffered sudden onset blindness emergency treatment to rapidly lower the blood pressure may be recommended. Blood pressure must be measured regularly whilst this emergency treatment is given to ensure blood pressure does not drop too low so your dog may need to be admitted to hospital during the first stages of emergency treatment. If treatment can be started at an early stage of the disease then there is a chance that your dog may regain its sight.

If an underlying cause can be identified and treated then blood pressure may return to normal without the need for any specific medication. Unfortunately in most cases this is not possible and additional drugs are needed to reduce blood pressure. Fortunately in most cases treatment is effective, and blood pressure can be brought into the normal range within a few weeks of starting treatment.

For the majority of animals treatment will be required lifelong and in all cases it remains important to continue to monitor blood pressure as accurately as possible in order to identify any recurrence of the problem.

Heart rhythm disturbance (atrial fibrillation)

There are many different heart problems that can affect dogs. Some of these affect the rhythm of the heart beat and one such condition is atrial fibrillation. This is most commonly seen in large and giant breeds of dog but can be seen in smaller dogs associated with heart disease. Atrial fibrillation does not cause any specific signs so it is unlikely that you will identify this as a cause of illness in your pet. However, any heart disease should be taken very seriously and an early visit to your vet can help to achieve a good outcome.

Atrial fibrillation is one type of disturbance of the normal heart rhythm (dysrhythmia). To understand this condition we first need to know how the normal heart functions:

In the normal heart electrical activity is initiated from a natural pacemaker in the heart and follows a set path around the heart muscle. As the electrical activity moves through the muscle the muscle begins to contract. The electrical signals move in an ordered way like a wave over the heart surface, from the chambers at the top of the heart (atria) to the lower chambers (ventricles). As the electrical signals pass through the heart muscle contracts in a synchronised fashion, like squeezing a tube of toothpaste.

The heart is divided into a left and right side and there are 2 chambers on each side (one atrium and one ventricle, linked together through a valve). In the normal heart the upper chambers (the atria) contract first squeezing the blood out of the atria and into the main pumping chambers, the ventricles. When the ventricles are full they begin to contract to pump blood around the body (from the left side of the heart) or around the lungs (from the right side).

Atrial fibrillation normally occurs in enlarged hearts where the atrial muscle is already stretched. Damage to the muscle caused by the stretching can make it more likely that a spontaneous electrical pulse will be generated in an area outside the pacemaker.

In atrial fibrillation there is disruption of the normal electrical activity throughout the atria resulting in random and chaotic atrial muscle contractions and preventing normal atrial contraction. The electrical pathways in the ventricles are still intact, allowing the ventricular muscle to contract in an organised manner. But because the electrical signals that the ventricles receive from the atria are random and so much more frequent and chaotic than normal, the ventricles often do not have time to contract and relax before a new signal arrives telling them to contract again.

Hence the contractions are not regular and there is a variable time between each heart beat. When you listen to a heart in atrial fibrillation you hear an erratic jungle drum beat rather than the regular lup-dup sound. Some people say that atrial fibrillation sounds like shoes in a tumble dryer.

Atrial fibrillation is normally a rapid heart rhythm and because the ventricles are contracting so often they do not have time to fully fill with blood between each beat. The amount of blood leaving the heart is therefore reduced and this poor blood supply can result in signs of lethargy and exercise intolerance and even exacerbate heart failure.

Atrial fibrillation is much more common in large and giant breeds of dog and in these breeds may even occur with an apparently normal heart. This may be due to the fact that these giant dogs naturally have such large hearts.

In smaller breeds of dogs atrial fibrillation usually only occurs in dogs with enlargement of the upper chambers of the heart (the atria). This enlargement of the heart can be caused by a variety of diseases but most commonly is caused by some congenital heart diseases (where the heart develops abnormally from birth), and dilated cardiomyopathy (DCM) or leaky heart valves (mitral valve disease) in older animals.

A few drugs (most notably digoxin, which may be used in the treatment of some heart diseases) can also cause atrial fibrillation. If your dog is receiving any medication make sure you mention this to your vet even if you think they already know.

In large and giant breed dogs atrial fibrillation may occur in apparently normal animals and there may be no outward signs of disease. Often in these breeds the condition is detected at a routine examination at the vets for an unrelated problem or at a routine health check. If underlying heart disease is present then you may first notice signs of this. Signs of heart disease can vary but may include: unwillingness to exercise; coughing at night or breathlessness on exercise.

Your vet will probably recognise that your dog has an abnormal heart rhythm when they listen to your dog’s heart. However, in order to confirm the diagnosis an ECG examination is essential to distinguish it from other types of abnormal heart rhythm.

An ECG is a simple test which records the electrical activity from your dog’s heart. If atrial fibrillation is detected then other tests are indicated to look for underlying heart disease. These tests will almost certainly include X-rays and ultrasound examination of the heart but sometimes blood tests are also required.

Even for a vet, it is very difficult to accurately assess heart rate in atrial fibrillation without an ECG. This is because some of the heart beats are so weak that they are very hard to hear with a stethoscope and do not result in a pulse that is strong enough to feel.

Although in people there are some treatments specifically aimed at converting the heart rhythm back to normal this is rarely undertaken in dogs. If there is an underlying heart disease then this requires management. Provided the heart rate is not too fast, dogs can perform reasonably well despite atrial fibrillation. If the average heart rate is rapid in a dog with atrial fibrillation, specific medications will be required to reduce the heart rate.

If the heart rate can be maintained at a roughly normal rate and the ventricles are able to fill properly before contraction they can deliver an adequate blood supply to the body tissues. In large or giant breed dogs with atrial fibrillation that is not too fast and no evidence for a heart condition can be found (this is sometimes referred to as “lone” atrial fibrillation), periodic retesting of heart size and function will be required. This is because in some of these dogs, especially Irish Wolfhounds, the atrial fibrillation is a warning that development of dilated cardiomyopathy is likely at some stage in the future (although it is much harder to predict when it will become obvious – this may be months or years from the time the atrial fibrillation was first detected).

It is unusual for dogs with atrial fibrillation to ever go back to having a normal heart rhythm. However, those dogs with “lone” atrial fibrillation (no detected underlying heart disease) sometimes live many years after diagnosis with no signs of disease, although they should be monitored periodically by your vet.

The outcome is not so good for those dogs with an obvious underlying heart problem. In these cases the heart disease is often severe enough that the dog will require cardiac medications for life and life span will be reduced.

If you have any concerns about our dog contact your own vet for further advice.

Heart disease: drug treatment

Heart disease does not necessarily mean heart failure. Many dogs with heart disease have no outward signs of illness and are able to lead relatively normal lives without any medication. However, most heart diseases will get worse and once symptoms start, treatment will probably be required for the remainder of your dog’s life.

In early stages of heart disease there may be no signs and your dog may just need to be checked regularly by your vet. However, in most cases heart disease does get worse and treatment may be necessary to relieve the signs of disease and slow down the rate of disease progression.

Management of heart disease requires a combination of:

  • Changes to your dog’s lifestyle, ie he may not be able to exercise as much and it is very important that he is always allowed to rest whenever he wishes.
  • Drugs to remove excess fluid retention (ACE inhibitors and diuretics).
  • Drugs to improve the strength of the heart beat (pimobendan) or change the heart rate (digoxin, other antiarrhythmics).
  • Dietary changes may be recommended by your vet depending on the type of heart disease present.

Heart valve disease

Many animals with mitral valve disease show no signs of heart disease and these patients require no specific treatment. However, heart failure may develop and then appropriate treatment can be started.

Heart muscle failure

In some heart disease the heart muscle itself is affected. It may become thin and weak, in which case drugs can be used to improve heart muscle contraction. In some disease the heart muscle becomes thickened and tense and drugs may be used to help the muscle relax so the heart can expand and fill with blood between contractions. In both cases it may be useful to also give drugs that reduce the resistance in the circulation so that it is easier for the heart to pump blood around the body.

Heart failure

Once the heart has failed for whatever reason, fluid will start to build up. If the right side of the heart is failing fluid may accumulate in the abdomen or in the chest (outside the lungs). More commonly the left side of the heart fails and then fluid builds up within the lung itself.

Heart rhythm disturbance

Sometimes the diseased heart develops an abnormal rhythm. If the average heart rate is rapid, specific medications will be required to reduce the heart rate. If the heart rate is too slow then drugs that increase the heart rate or an artificial pacemaker may be necessary.

Not all drugs are appropriate in every animal and your vet will decide on the best treatment programme for your pet and will discuss treatment options with you. Often a combination of drugs is needed and the doses of drugs may change with time. Usually once treatment has started it will need to be continued for the rest of your pet’s life. All drugs have some side effects and if you are worried about any aspect of your pet’s treatment or any of the signs it is showing you should contact your own vet for further advice.

For most diseases, there is no evidence that it is beneficial to start treatment before signs of heart failure develop.

There are many drugs that can be used to help animals with heart failure. Most commonly a combination of a diuretic, an ACE inhibitor and pimobendan is used.

Diuretics (also sometimes known as ‘water tablets’)

These are used to stop fluid retention, which can cause breathing difficulty if it builds up in the lungs. Diuretics help to remove water from the body by increasing the production of urine.

The most commonly used diuretic is furosemide. Furosemide is usually given 2 or 3 times daily. In some more advanced cases other weaker diuretics may be used in combination with furosemide to improve the effect (i.e. spironolactone, hydrochlorothyazide).

Since animals on diuretics will produce more urine they will also need to drink more water. It is important that you do not restrict the water intake of your pet as they may become dehydrated. Animals receiving diuretics will need to urinate more frequently and sometimes can develop urinary incontinence – either making puddles in the house or leaking small amounts of urine when lying down. As the excess water is washed out of the body it also carries with it some salts and animals receiving diuretics for a long time may become a bit deficient in some salts.

Your vet will want to test blood samples from your pet to ensure that they are not developing problems as a consequence of the diuretics but you should not give any other supplements without veterinary advice. If you notice any side effects when your pet is given diuretics you should discuss these with your vet.

ACE inhibitors

There are many drugs in this group and they act by dilating blood vessels, which results in a lowering of blood pressure. In people these drugs are used frequently to treat high blood pressure – in pets they are most often used in heart failure to help prevent fluid retention and make it easier for the heart to pump blood. The most commonly used drugs in this group are enalaprilbenazeprillisinopril and ramipril. These are usually given once or twice daily.

When these drugs are first given it may take your pet some time to get used to the medication, Since these drugs lower blood pressure your pet may suffer signs of lethargy or weakness and very rarely even collapse. If these signs develop when you start the medication, contact your vet immediately to get further advice.

The most serious side effect usually seen with these drugs are effects on kidney function. For this reason, if your pet is prescribed ACE inhibitors, your vet will probably recommend some routine blood tests to make sure your pet’s kidneys are working normally before, and during treatment. Vomiting and diarrhea may also be seen in some animals.

ACE inhibitors should not be given to pregnant animals as they can cause birth defects.

Drugs to improve heart function

Pimobendan is most often used in dogs with heart valve disease or those with dilated cardiomyopathy. It improves the efficiency of heart function by increasing the force of heart contraction (without increasing the use of energy and oxygen by the heart muscle) and causes blood vessel dilation (which makes it easier for the heart to pump blood around the circulation).

It is often used in conjunction with other drugs in the management of heart failure. Side effects are rare but may include vomiting or irregular heart rhythms and if these occur the dose may need to be reduced. It is usually given twice daily, ideally 1 hour before feeding.

Antiarrhythmic drugs

Beta Blockers

Beta blockers slow the heart rate and therefore reduce the amount of oxygen needed by the heart muscle. They can also be used to slow the heart in some rhythm disturbances. The most commonly used beta blockers are propranolol and atenolol and these are given once or twice daily.

Beta-blockers may cause low blood pressure, low heart rate and worsen heart failure. Diarrhea may also occur. To reduce the risk of side effects beta blockers are usually given at a low dose to start with and the dose is increased slowly until it has the required effect. Signs to look out for that might indicate an overdose of beta blockers are lethargy, weakness or collapse, or a worsening of signs of heart failure. If you are worried about any signs in your pet call your vet for advice.


Digoxin has mild effects on the heart muscle making it contract more strongly. In the past this drug was used commonly to treat heart failure for this property. However these effects are so mild that nowadays this drug is used mainly for the treatment of heart rhythm disturbances, particularly one called atrial fibrillation. It causes the heart to slow down. This drug is usually given twice a day and a liquid form is available as well as tablets.

A few days after starting digoxin your vet will want to test the drug levels in the blood. The sample has to be taken 6-8 hours after administration depending on the lab analyzing the sample. Side effects of digoxin commonly include a loss of appetite and vomiting, diarrhoea and depression. If these signs develop you should contact your vet immediately for advice. Drug levels and kidney function must be routinely monitored (i.e. every 3 months) to make sure they are not above the therapeutic range and that your pet is not at risk of side effects.


Diltiazem is used in some pets with an abnormal heart rhythm to slow the heart rate. It is commonly combined with digoxin to treat atrial fibrillation. Your vet may want to check that your pet’s liver and kidneys are working normally before they prescribe this drug. Tablets are usually given 3 times daily.


Sotalol is used in some pets with an abnormal heart rhythm to slow the heart rate. Side effects may include low blood pressure, low heart rate, depression, nausea, vomiting and diarrhea. If these signs develop you should contact your vet immediately for advice. Your vet will want to check kidney function before prescribing this drug. Tablets are given twice daily.


Amiodarone is used in some pets with an abnormal heart rhythm to slow the heart rate. In most cases it is used when other antiarrhythmic drugs have failed. Dogs on this drug may lose appetite and vomit. Other side effects may include low blood pressure, low heart rate, low thyroid hormone levels and liver toxicity. Your vet will want to do some blood tests to check that your pet does not have liver disease before prescribing this drug and will want to repeat these tests periodically while on treatment. Tablets are usually given twice daily.

Heart disease in your dog

Heart disease is increasingly common in dogs – probably because their average life expectancy is increasing due to improved veterinary care. Some heart defects, e.g. hole in the heart, are present from birth (congenital heart defects) but only cause signs as the dog gets older. Other diseases develop later in life as a result of the effects of ageing or damage to the heart. The most common heart diseases in the dog develop as the dog ages and its heart starts to wear out.

The dog’s heart, like that of humans, is a muscular pump with four separate chambers. The right side of the heart sends blood to the lungs where it picks up oxygen. The left side of the heart pumps the blood around the body. The four areas of the heart are separated by valves which ensure that blood always flows in the correct direction through the heart.

Heart disease may affect any area of the heart:

Heart valves

The valves within the heart may fail to develop properly, e.g. mitral dysplasia, or may degenerate as a result of ageing (endocardiosis). Specific infections can affect the heart valves (endocarditis). Abnormal valves allow leakage of blood between heart chambers even when they are closed. When valves leak abnormal blood flow can be detected when listening to the heart (a murmur) and on ultrasound.

Heart muscle

In general terms the heart muscle may be either too thick or too thin. If the muscle is too thin the heart is unable to contract properly and if the muscle is thick the heart cannot relax and therefore does not fill with blood between contractions. In either case the heart is unable to pump sufficient blood out.

Electrical conduction

Abnormal electrical conduction affects the rate and rhythm of the heart. Electrical abnormalities can be caused by disease outside the heart. If the heart beats too quickly there is not enough time for it to fill properly between beats and so it pumps less blood with each beat. If the heart beats too slowly there are not enough pulses to supply enough blood to the body. Chaotic rhythms occur where contractions of different parts of the heart are not synchronised and so pulse volume is reduced.


The pericardium is a strong sac that surrounds and supports the heart. Changes to the pericardium usually result in constriction of the heart, preventing it from filling properly between contractions. The right side of the heart (because it has thinner walls) is usually more easily compressed than the left.

Heart disease in older dogs is usually caused by damage to the heart valves or stretching of the heart muscle. Particular breeds of dog are more prone to certain types of heart disease.

The two most common types of heart disease in the adult dog are:

Valvular heart disease

This is particularly common in Cavalier King Charles Spaniels (CKCS) but can occur in almost any breed. As a dog ages its valves may become worn and degenerate and therefore get more and more leaky. Instead of closing properly each time the heart pumps, the valves flop open allowing blood to move backwards as well as forwards through the heart chambers. This results in a reduced blood supply to the body. More about mitral valve disease.

Dilated cardiomyopathy (DCM)

This form of heart disease is seen most commonly in large and giant breeds, particularly Dobermann pinschers, Great Danes and Irish Wolfhounds. Some spaniels are also affected and it could rarely affect dogs of any breed. The disease causes a stretching of the heart muscle walls so that the heart swells (like a balloon filled with water). The contractions of the heart muscle become very weak so blood is not pumped around the body effectively. More about dilated cardiomyopathy (DCM).

In humans, heart disease is the result of damage to the heart muscle caused by blood clots (myocardial infarction) anf this causes the signs of a heart attack. However, dogs do not get this kind of heart disease.

The signs of heart disease are often very similar whatever the cause. Many of the signs of heart disease can be confused with natural ageing changes. Reduced energy and less desire to exercise are common. Dogs with severe heart disease often have poor appetites and may lose weight. If water retention occurs as a result of the heart failure you might not notice that your dog is losing weight.

Other common signs of heart failure are panting and coughing due to fluid build up in the lungs – but remember these signs may be seen with many other diseases too. Less commonly, dogs with heart disease may faint or collapse.

When your vet examines your dog he will use a stethoscope to listen to your dog’s heart. If heart disease is present, your vet may hear a change in the heart sounds. The heartbeat may be fast (or occasionally slow), irregular or there may be an unusual noise (a murmur).

X-rays may show that the heart is enlarged and ultrasound can be used to see whether the heart muscle and valves are working normally. An electrocardiogram (ECG), records the electrical activity that causes the heart muscle to beat and can be used to see if the beat is irregular.

Ask your vet to check a new puppy as soon as you get it and they will listen to its heart to detect any possible congenital heart problems. You may want to return the puppy to the breeder (if you are not already too attached to it) or, if possible, consider early correction of defects before signs of disease develop.

Heart disease does not necessarily mean heart failure. Many dogs with heart disease have no outward signs of illness and are able to lead relatively normal lives without any medication. However, most heart diseases will get worse and once symptoms start, treatment will probably be required for the remainder of your dog’s life.

In early stages of heart disease there may be no signs and your dog may just need to be checked regularly by your vet. If signs develop these can be treated. However, in most cases heart disease does get worse and treatment will only slow down the rate of disease progression. Such treatment includes:

  • Changes to your dog’s lifestyle, i.e. more controlled exercise.
  • Drugs to improve the strength of the heart beat or change the heart rate (digoxin, pimobendan or antiarrhythmics).
  • Drugs to remove excess fluid retention (ACE inhibitors and diuretics).
  • Dietary changes may be recommended by your vet depending on the type of heart disease present.

Some congenital heart defects can be corrected by surgery. If your vet recommends surgery it is well worth considering. If the problem is corrected at an early stage (before any signs develop) it may be that your dog could be cured and never require any further treatment.

This is an impossible question for your vet to answer. Some animals with heart disease may live normal lives with no symptoms at all. Other dogs do not respond to any treatment and may die quickly. It all depends on the type and severity of the heart disease. Your vet may be able to give you an idea of the likely lifespan of your pet on an individual basis.

The most important thing when managing any disease is the quality of life that your dog has. If you are concerned that your dog is feeling unwell, or consider that the treatment is not helping him, you must contact your vet for further advice.

Dilated cardiomyopathy (DCM)

Dilated cardiomyopathy (DCM) is a disease affecting the heart muscle. It is the second most common heart disease in dogs (after mitral valve disease). In DCM the heart is unable to contract normally and as the muscle stretches the heart gets larger. DCM affects mainly middle-aged large and giant breed dogs and some spaniels. Small breeds of dog are occasionally affected. Male dogs are more likely to be affected than females. Animals with DCM usually develop signs of heart failure and abnormal heart rhythms.

Cardiomyopathy literally means disease of the heart muscle (cardio = heart, myopathy = muscle disease). In DCM the heart muscle becomes thin and weakened. The heart muscle can be damaged in a number of ways including viral infections.

Dietary deficiencies of taurine (an essential amino acid only found in meat protein) and carnitine have been reported as causes of DCM in some groups of dogs. Low levels of carnitine in the blood has been detected in some Boxers and springer spaniels with DCM, and some Cocker spaniels with DCM may have low blood taurine levels.

Since the disease is much more common in some breeds than others, genetic factors are probably important. In most cases of DCM there is no apparent cause of the damage to the heart and this is termed idiopathic cardiomyopathy.

Once the heart muscle is damaged it becomes weak and so does not contract well. Because heart contractions are weak the heart does not empty with each contraction and the blood supply to the body is reduced. Pulses are weak and the paws may feel cold. With time the heart muscle stretches and heart becomes a flabby sac.

DCM eventually results in heart failure with fluid build-up in the lungs (pulmonary oedema), the chest (pleural effusion) and belly (ascites).

Signs of heart disease are often not noticed by owners until their pet develops heart failure. Your vet may hear an irregular heart beat on a routine examination and this may be the first sign that your dog has heart disease.

Owners most commonly recognise exercise intolerance and breathlessness in their pet but anorexia, depression and excessive drinking are also common. The first sign in many dogs is coughing and collapse.

You may notice that your dog has recently lost weight – this may be due to cardiac cachexia. If ascites develops the abdomen may be distended and you must be careful not to misinterpret this swelling as weight gain. Some animals with DCM die suddenly.

From the changes that you describe and by examining your dog your vet may suspect that your pet has a heart problem. Other tests will be needed to confirm this. Chest X-rays may show that the heart outline is enlarged and there may be other changes (such as fluid in the chest) caused by heart failure. Y

our vet will need to examine your dog’s heart with ultrasound to make the diagnosis. With ultrasound it is possible to measure the thickness of the heart muscle and the size of the heart chambers. Ultrasound also allows us to see the heart beating and we can measure how much contractility it has.

Abnormal heart rhythms are common in DCM so an electrocardiogram (ECG) is useful in patients with DCM. A special type of rhythm (atrial fibrillation) is present in most giant breeds with DCM and other disturbances to the heart rhythm are particularly common in Dobermanns and Boxers.

Blood changes in DCM are not specific, but may indicate poor kidney function due to reduced blood supply to the kidneys. There is now a blood test (proANP) that can be used for early detection of heart disease in dogs and this may be useful in some cases if other diagnostic methods are not available.

In almost all cases there is no treatment for the underlying muscle disease. Signs of heart failure can be managed according to its severity. Patients in acute heart failure (collapsed and with breathing difficulties) should be taken into hospital for strict rest and immediately started on diuretics and a vasodilator (nitroglycerine cream rubbed onto the ear pinna). Intravenous diuretics are given to remove fluid on the lungs.

Long-term treatment includes controlling exercise and administering oral diuretics and ACE inhibitors to reduce lung fluid. If the heart rate is fast then dogs may benefit from drugs that slow the rate. Pimobendan has been shown to improve quality of life in some dogs with DCM.

If your vet thinks that a dietary deficiency is a possibility then supplementation with carnitine or taurine may be beneficial. However, these treatments can be expensive in giant breeds and are unlikely to beneficial in these breeds. If you can afford it, it is probably wise to try supplementation with L-carnitine in Boxers and Springer Spaniels and taurine in Cocker Spaniels and dogs on vegetarian diets.

If heart rhythm is abnormal drugs may be given to control this. It is very unusual to be able to convert the heart back to a normal rhythm if DCM is present but if the heart rate is slowed the heart may contract better with each beat and therefore give a better output of blood to the body.

Kidney function, and other blood tests should be performed regularly in patients receiving treatment.

The outlook for most dogs with DCM is not very good. Most animals with DCM develop heart failure and some die, as fluid builds up in the lungs, or are put to sleep as a result of poor quality of life. Many dogs with DCM die suddenly (probably as a result of developing severe cardiac rhythm disturbances).

The outlook for dogs with DCM is extremely variable depending on the severity of the disease and the breed of dog. Most dogs survive around 6 months and around one-third of dogs will be alive one year after diagnosis. Cocker Spaniels and giant breed dogs appear to survive better than other breeds. Some, with appropriate management, may live relatively normal lives for years after diagnosis.

Dogs with fluid in their chest at the time of diagnosis tend not to survive so long. The outlook for most Dobermanns is unfortunately extremely poor (with many only living a few weeks and most only living a few months after diagnosis).

Congenital heart diseases

Bringing a new puppy into the family is an exciting time and should be a time of great joy. It can be particularly distressing to find that your new arrival has a problem. It is important that you get your new puppy checked over by your vet so that any obvious problems can be identified before you become too attached to it.

Congenital defects are caused by abnormal development of the foetus and disease is present from the time that the animal is born. However, although the disease is present from birth, signs may not be noticed until later in life. Congenital defects can occur in any part of the body and the heart is no exception. The heart is a complicated structure and as it develops there are many things that can go wrong.

Around 1 in 200 dogs have a congenital heart problem. No-one knows why the heart develops abnormally in some animals. It is probably usually the result of a combination of environmental conditions and genetic factors. Some diseases are more common in particular breeds and so it is likely that they are partly passed from parents to offspring. For this reason animals with congenital diseases should not be allowed to breed.

If defects are severe then signs can be marked, but in some cases you may not even know that there is anything wrong with your pet. Often one of the first signs of a heart defect is a heart murmur detected by a vet during routine examination.

When you buy a new puppy you should take them to your vet so that your vet can check them over. Your vet should listen to their heart and will be able to tell if a murmur is present. However there are some diseases that cause no signs in the early stages.

If heart disease progresses then an animal with a congenital condition can go on to develop heart failure. This may occur relatively quickly within the first few weeks or months of life if the defect is serious. However in many cases no signs are shown until the animal reaches adulthood.

There are a number of congenital heart diseases and some of these more commonly affect some breeds of dogs than others. The diseases are caused by abnormal development of the blood vessels (abnormal connections or narrowing), the valves or as a result of abnormal connection between different parts of the heart (hole in the heart).

The most common forms of congenital heart defect include PDA (patent ductus arteriosus) where there is a communication between blood supply into and out of the heart; narrowing of the large blood vessels taking blood away from the heart – to the lungs (pulmonic stenosis) or to the body (aortic stenosis). Sometimes there is abnormal development of the valves between the various chambers of the heart usually affecting the mitral valve (mitral dysplasia). It is rare for dogs to have a ‘hole on the heart’.

If your vet detects a heart murmur on examination they will need to do further tests in order to find out what is causing the problem. X-rays might help but ultrasound will be needed to find out exactly what is wrong with the heart. Your vet may need to refer your pet to a vet who specialises in heart disease for detailed examination. This will allow the best treatment plan to be formulated.

Unfortunately the long-term outlook for animals with severe congenital heart disease is usually not good. The only cure for heart defects is surgical correction. Some defects can be corrected by an operation, for example to tie off an abnormal blood vessel – for other defects there is no specific treatment.

In cases of pulmonic stenosis it may be possible to reduce the narrowed valve by stretching it using a special catheter (balloon valvuloplasty). In some cases animals have no problems with their disease and can live with the condition.

If animals develop heart failure then this can be managed with drugs to control signs.

If your pet can have surgery to correct their heart defect they will probably need to be sent to a specialist surgeon. However recovery from the operation is usually rapid and they may be back to normal in a week or two.

Unfortunately if there is no surgical option for your pet then they may need drug treatment for the rest of their life. It can be very distressing to watch a young animal suffer with heart disease and, if there is no treatment for your pet, you should discuss with your vet whether euthanasia might be the kindest option.

Canine heart testing schemes

Congenital heart diseases are not uncommon in puppies and some of these are inherited. Pedigree dogs have many inherited diseases and different breeds each have their own problems. Many dog breed societies employ testing schemes to detect individuals affected with certain conditions at any early stage of the disease at an early age. Early detection is important, not only to ensure appropriate treatment for affected dogs but also so that these animals can be excluded from breeding programmes to prevent them passing on the disease to their offspring.

There are a number of breed testing schemes which allow early detection of these conditions. The following breed clubs operate heart testing schemes:

  • Boxer: aortic stenosis
  • Bull terrier: aortic stenosis and mitral dysplasia
  • Cavalier King Charles spaniel: mitral valve disease
  • Great Dane: dilated cardiomyopathy (DCM)
  • Irish Wolfhound: dilated cardiomyopathy (DCM)
  • Newfoundlands: aortic stenosis
  • Pyrenean sheepdog: patent ductus arteriosus (PDA)
  • Field Spaniel: prevalence of murmur and arrhythmia

Heart testing for the breed schemes can only be carried out by certain specialist veterinary cardiologists. A list of all currently eligible vets (and their contact details) can be found on the Veterinary Cardiovascular Society website:

An appointment can be made with a specialist veterinary surgeon in your area at their practice or, in some cases, the specialist may come to your vet’s practice. Additionally many of the breed clubs arrange for specialists to be available at certain major dog shows – you should contact the individual breed societies for information on this.

There are a number of advantages to the breed club of running these schemes:

  • The clubs can identify unaffected (or less severely affected) animals which can then be used for breeding.
  • The number of affected dogs in the breed can be calculated so that clubs can monitor whether the disease is becoming more or less common and whether the breeding programmes are working.
  • To identify affected animals so that owners and vets caring for these animals can be advised on treatment.

The exact format of the investigation will depend on the individual breed scheme. The three standard tests used for investigation of heart disease are:

Listening to the heart with a stethoscope (auscultation)

Using a stethoscope the vet can identify any heart murmurs and abnormal heart rhythms which may indicate a structural defect in the heart. In many cases detection of an abnormality with a stethoscope will indicate that further investigation is required.

Performing an ECG

An ECG allows monitoring of the heart rhythm and rate. Some breeds of dog, notably boxers and dobermanns, develop heart conditions that specifically affect their heart rhythm. Sometimes your vet will be able to perform an ECG in the surgery but for many conditions it is necessary to fix a mobile device to the dog which is worn for 24 hours or longer the device is then removed and the information sent away for analysis.

Ultrasound of the heart

Specialist veterinary cardiologists can use ultrasound to examine the heart in detail. This can be done in most dogs without any form of sedation or anaesthesia and in some breeds it can be done without clipping the hair. With ultrasound the vet can examine the chambers and valves of the heart to detect any abnormalities in heart development or function.

Screening tests are very sensitive in picking up early changes in the heart. It is quite possible that the vet doing the test will detect an abnormality that will not affect your dog in everyday life (however it still might mean that your dog cannot be used for breeding).

The vet who does the screening will provide a report to your usual vet and any further investigation or treatment will be managed through your own veterinary surgeon. In some cases your vet will want to refer your pet to a specialist veterinary cardiologist for further investigations.

When animals are screened through a breed heart testing scheme the results of the tests will also be sent back to the breed society for them to use in monitoring the health of the breed. This information will always be kept confidential.

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Hypothyroidism (Thyroid hormone deficiency)

Thyroid hormone is produced by a small organ in the neck. A lack of this hormone (hypothyroidism) may cause a whole range of problems. Dogs with this disease are often mistakenly thought to be just getting old. It is worth looking out for this disease because treatment is simple – with daily tablets to replace the missing hormone your dog could be given a new lease of life.

The thyroid gland is a small organ in the front of the neck just around the voice box. This gland makes thyroid hormone and releases it into the blood in a carefully controlled way. Just the right amount of hormone is released in order to keep your dogs body working at the right rate.

Thyroid hormone is essential for the normal functioning of the body, affecting almost all cells and organs. It is particularly important for controlling the heart rate and the activity of cells. When there is more thyroid hormone the cells work harder and burn more energy, when there is less the whole body slows down.

There are a number of reasons why a dog might not produce enough thyroid hormone. In most dogs, it is just because the thyroid gland has been damaged and does not work as well as it should. Very rarely the problem can be due to a cancer of the gland or abnormal development of the hormone system in a puppy.

A lack of thyroid hormone in the body is called hypothyroidism. Often the symptoms of a lack of thyroid hormone are not very obvious. The problem is usually seen in middle-aged or older dogs and quite often the symptoms come on so slowly that owners simply think their dog is just getting a bit old. Dogs tend to slow down a bit and be less keen to run around. Additionally, their appetite is usually normal but they may put on weight because they are not exercising normally.

Other common changes associated with the disease are bald patches on the body, other skin problems, or feeling the cold more than normal. Sometimes dogs with long coats (like Retrievers) don’t moult properly and get shaggy, matted coats.

This disease can be a bit tricky to diagnose. Blood tests and skin biopsies can help your vet, but most often the final proof is found by measuring the level of thyroid hormone in the blood.

There is no treatment which will make your dog’s thyroid gland start to work normally again. However, it is very simple to replace the missing hormone by giving hormone replacement tablets. These tablets will need to be given at least once (and often several times) every day for the rest of your dog’s life. However, once your dog is receiving these tablets they should get back to their normal self very quickly.

Your dog should be happier and more active within a few weeks and if they had other symptoms (like skin disease) this should get better within a few months. Your vet will probably want to keep a check on your pet and may need to take several blood samples to ensure that the tablets are working properly but, after this, the long term outlook for your dog is very good.