Heart Defects in Cats: Everything You Need to Know

Heart failure is a broad term that encompasses a variety of disease states of varying degrees.

Many people may have mild heart defects that do not cause any problems at the moment and often do not need to be medicated, but some heart defects worsen over time and can eventually lead to heart failure, which means that the heart can no longer do the work required.

Heart defects are often divided into two categories: Congenital (congenital) heart defects, which are malformations and acquired heart defects that you get later in life. Both congenital and acquired can be hereditary.


Examples of the most common congenital heart defects are:

  • Septum defect (atrial or ventricular septal defect): hole in the wall between the right and left ventricles or right and left atria
  • Dysplasia (mitral or tricuspid dysplasia): malformed valves between atrium and ventricles on left or right side
  • Stenosis (aortic or pulmonary stenosis): narrowing of the aorta or large pulmonary artery where they exit the heart)

There are several other, more uncommon malformations. The malformations can be differently severe with different prognosis. Sometimes several different malformations occur in the same patient. Some types of malformations are more common in some breeds.

Acquired heart disease in cats is:

  • HCM (hypertrophic cardiomyopathy): Thickened wall of the left ventricle. Two mutations have been found in cats (Maine Coon and Ragdoll) that are linked to HCM, but there are probably more that have not yet been discovered. In humans, there is a similar disease and more than 450 different mutations that produce HCM have been identified. Some cats, mainly older people, get tumors in the thyroid gland, which causes an abnormal increase in thyroid hormone in the blood. These cats can have changes that on ultrasound are similar to primary HCM, but are reversible and disappear when the original disease is under control. Kidney failure and high blood pressure (hypertension) can also cause similar heart changes.
  • DCM (dilated cardiomyopathy): The heart muscle, especially in the left ventricle, becomes weakened and does not contract normally, causing the heart to become enlarged. DCM was previously seen in cats that did not get enough of the amino acid taurine in their diet. Today, DCM is uncommon in cats since feed manufacturers began adding taurine to cat food.
  • Mitral insufficiency (leakage in the valves between the left atrium and ventricle): Leakage in the valves can occur with age. In cats, the leak is rarely so severe that it causes heart failure, but a wheezing sound can occur.
    There are also a small number who have wheezing without being able to detect anything wrong with the heart. The blowing sound can then be due to the heart pumping unusually powerful, or that there are changes that are so mild that you cannot detect them with ultrasound.


The most common sign of heart disease is wheezing. In the case of a congenital malformation, the wheezing sound is often already present in the little kitten. In some cases, the wheezing sound is mild in the beginning and becomes more prominent as the heart grows.

In some cases, it may be milder or disappear completely.

In HCM, wheezing is reported in about two-thirds of patients.

Typical of these cats is a wheezing sound that is heard more clearly when the heart beats hard and that can completely disappear when the heart beats calmly. However, having a wheezing sound does not necessarily mean that you feel sick to your heart.

If the heart defect is severe enough, it can cause various symptoms such as weakness, fainting – often in connection with exertion, difficulty breathing, bulging, emaciation and signs of blood clots. With plugs, the symptoms vary depending on where the plug is located.

Clots usually settle in the large carotid artery (aorta) where it divides into the hind legs.

The hind legs then do not get enough blood, which causes pain, movement problems and cold hind paws. If clots settle in other places, such as the lungs or kidneys, they can be difficult to detect. You can read more about symptoms during heart failure.

Some cats live with heart disease all their lives without feeling any symptoms.

What can you do yourself?

Before buying a cat, make sure that it is checked by a veterinarian without any signs of heart disease.

Breed clubs can inform if the breed in question is particularly prone to any heart disease. In that case, control programs can be available for breeding animals and you should then examine the status of parent animals before deciding to buy a kitten.

Many purebred cats intended for breeding are tested for HCM to try to avoid spreading the disease further. However, one should keep in mind that HCM can develop at any time in life and a cat that has been tested without a complaint can develop the disease later.

It is advisable to have the veterinarian listen to your heart at some point in the year so that you know if a wheezing sound has occurred that has not existed before.

If you mainly feed your cat homemade food, it is important to make sure that the cat gets enough taurine to prevent it from developing DCM.

When should veterinarian be seen?

If a wheezing sound or any of the above symptoms that raise the suspicion of heart disease is detected in your animal, a cardiac examination by a specially trained cardiologist is recommended. If your own veterinarian does not have that competence, he or she can refer you to a specialist who investigates and gives advice on possible treatment and follow-up.

As many heart diseases worsen over the years, it is common to perform follow-up examinations annually to assess whether treatment should be initiated.

If the symptoms suggest heart failure (rapid breathing at rest – more than 30 breaths per minute, shortness of breath, collapse, signs of blood clots in the hind legs or affected general condition), you should contact a veterinarian as soon as possible as the condition can be life-threatening.

If you intend to use your cat in breeding, you should check that it does not have a buzzing sound and, where relevant, participate in control programs before mating.


A cardiac examination always includes listening to the heart with a stethoscope (auscultate), usually ultrasound (echocardiography) and sometimes also X-rays, ECGs and blood tests depending on symptoms.

Treatment Many patients with heart defects do not need treatment, at least not early in life. Most patients who need treatment for their heart defect receive medication. The treatment is specially adapted for each individual depending on the type and degree of heart defect and the symptoms that have occurred.

The treatment may need to be modified over time if the heart defect worsens. Regular inspections are needed to assess this. The veterinarian then gives instructions on appropriate treatment.

For cats whose heart changes have been caused by another disease (usually hyperthyroidism / hypothyroidism or high blood pressure), treatment focuses on getting these primary diseases under control, after which the heart usually normalizes. Temporary cardiac medication may be needed while treating the triggering disease.

The prognosis is very variable for different heart patients. Unfortunately, heart defects can become so serious that despite the treatment, you can not give the cat a good quality of life. Then, for animal welfare reasons, you may be forced to let your friend fall asleep.

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