Cats have a reputation of being aloof and elusive creatures. But those of us who share our lives with a cat, know that when they are with their favourite people, they can be very open and loving animals. However, despite this closeness, cats can be very adept at hiding illness. In the case of the feline heart for instance, it can be difficult for an owner to notice disease until heart failure occurs.

Understanding Heart Disease

The heart is a muscular organ divided into four chambers. It has a central muscular septum which splits left from right, and valves which split the upper atrium from the lower ventricle. Blood can move in, through and out of these chambers when the heart muscle contracts during a heartbeat.

Cardiomyopathy refers to disease of the heart muscle and can be present from birth (congenital) or develop with age (acquired). A primary cardiomyopathy affects the heart muscle directly and has either a genetic or unidentified cause (referred to as idiopathic). Secondary cardiomyopathy results from disease elsewhere in the body and has an identifiable cause. Although there are many potential triggers of secondary cardiomyopathies, most cats diagnosed with heart disease will have a primary cardiomyopathy.

Types of Cardiomyopathy

Cardiomyopathy can alter the structure and function of the heart in different ways. 

Hypertrophic cardiomyopathy (HCM)

The most common acquired change to occur in cats is thickening of the heart wall and septum, especially around the left ventricle. This is called hypertrophic cardiomyopathy (HCM) and is most often diagnosed around 6 years of age.

Domestic shorthairs are most likely to develop HCM, but there are several popular purebred cats identified with a hereditary form. These include the large breeds (Norwegian Forest and Maine Coon), Ragdoll, Persian, British Shorthair, and Bengal. With this form of HCM, affected cats are typically diagnosed within the first 15 months of life. Genetic testing and screen testing (e.g. periodic blood tests or heart scans) have been developed for the Maine Coon and Ragdoll breeds, so your vet can advise if this is an option for your pet.

Restrictive cardiomyopathy (RCM) 

This form of cardiomyopathy results from scar tissue forming in the heart muscle, known as fibrosis. RCM usually affects the muscle around the left ventricle. HCM and RCM have similar effects on heart function, so any symptoms they cause will also be similar.

Dilated cardiomyopathy (DCM) 

This is now a rare cause of feline heart disease that involves thinning of the heart muscle and enlargement of the chambers. It can occur with a deficiency in the essential amino acid taurine which cats must consume in their diet. Commercially available, fully balanced cat foods will contain taurine, but owners who prepare a home-made diet should consult with a veterinary nutritionist to ensure their cat’s nutrient needs are being met.

Symptoms of Heart Disease

It is possible for your cat to have heart disease and show no apparent symptoms. In fact, heart disease is often detected on a pet wellness exam such as an annual vaccination visit, or when investigating symptoms related to another disease. The most likely sign that your vet will notice is a heart murmur.

Abnormal heart muscle alters blood flow through the chambers, creating an added sound in between the heart beats. Your vet can hear this murmur through their stethoscope during a heart assessment. Less commonly, your vet may notice an abnormal heart rhythm, known as an arrhythmia. This could be a heart rate that is slower or faster than normal or may involve missing or irregular heartbeats.

Heart murmurs are occasionally detected in kittens, but many disappear within the first 6 months of life. This type of murmur is sometimes called an innocent murmur, but your vet will discuss it with you if they suspect it is caused by something more serious. Congenital heart defects or reduced function may not be immediately obvious but if the heart cannot function adequately as the animal grows, affected young will fail to thrive, have stunted growth, and will have a low tolerance for play. 

Weight loss and lethargy can occur with heart disease but are more typical of diseases causing secondary cardiomyopathy. An overactive thyroid gland in senior and geriatric cats is one of the most common of these. Excess thyroid hormone production is associated with high blood pressure and weight loss and can cause changes in the heart muscle similar to HCM.

Understanding Heart Failure

Congestive heart failure (CHF) occurs if disease overwhelms the function of the heart and usually affects only one side. With left-sided heart failure, pressure changes create fluid leakage into or around the lungs. Right-sided failure may cause fluid build-up in the abdomen, but this is much less common in cats.

Heart failure will almost always be symptomatic. Symptoms may be gradual, and easy to overlook initially, or they may be sudden and dramatic. It may even be acutely fatal with no prior signs of disease. Whether you know your cat has heart disease or not, regular wellness exams and seeking veterinary treatment whenever your cat is not their usual self is an important step in staying on top of your cat’s health.

Symptoms of Heart Failure

Fluid build-up with CHF restricts the ability of the lungs to inflate or fill adequately with air, making breathing more difficult. When the fluid is within the lung tissue, it is known as pulmonary oedema. When it is around the lungs rather than within it, it is known as pleural effusion. Breathing changes may be as subtle as a change in rate or depth, or as dramatic as laboured, open-mouthed breathing.

In cats, one of the risks of heart disease is developing blood clots (thromboembolism). These occur in about 15% of cats with HCM and can develop in the absence of heart failure. If a clot gets lodged in a blood vessel it can starve a portion of the body of vital oxygen causing extreme pain, and tissue death. The most common location for a clot to lodge is in the blood vessel supplying the hindlimbs or one of the forelimbs. This causes weakness or paralysis of the affected leg in a cat that is also vocal and distressed from pain.

Breathing difficulty and thromboembolism are life-threatening and require emergency treatment at your vet clinic. This may involve several days of intensive care away from home and can be a distressing time for you and your pet. If you have concerns with how your cat will cope throughout this, your veterinary team can talk these through with you.

Diagnosing Heart Conditions

If your vet suspects your cat has heart disease, there are several tests they may recommend. Blood tests can check for causes of secondary cardiomyopathy, and blood pressure may be taken. If there is an arrhythmia, an electrocardiogram (ECG) may be performed to find the cause. However, the main method of diagnosing the type and severity of cardiomyopathy, is an ultrasound called an echocardiogram.

If your cat has CHF, a chest x-ray can assess what type of fluid build up is occurring and whether that fluid can be physically drained. This may be performed in an emergency before other tests are recommended.

Caring for a Cat with Heart Failure

Management of heart failure means symptom control. There is little evidence that medication prevents heart failure occurring. If your symptomatic cat is stable enough to be treated at home, there are a few medications that your vet might prescribe. Medication can suppress fluid build-up in the chest, improve the heart’s ability to pump blood, or reduce the risk of blood clots. High blood pressure or other diseases which compromise heart function may need additional treatment.

Getting them used to taking medication is an important part of caring for a cat in heart failure. Several medications are in tablet form. A liquid or flavoured option may be available but is not always the case, and it is important to check with your vet if there are any restrictions on giving medication with food. 

Aside from regular vet visits to assess treatment response, an easy way to monitor your cat’s condition at home is by measuring their resting breathing rate. When your cat is asleep or at rest, count how many breaths they take per minute. Record this and periodically recheck it. If their resting breathing rate is over 40 per minute, or if you notice the numbers progressively going up over time, take them for a check-up.


Heart failure cannot be cured but early detection of heart disease and recognising the symptoms of heart failure give your cat the best chance of having their condition controlled. Routine wellness exams are a great way for your vet to monitor your cat’s health and being heart savvy can help you look out for your cat at home.


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