Heart Disease in Cats

What is heart disease?

Also known as cardiovascular disease (CVD), heart disease is a collective term for diseases that affect the heart and the heart vessels. Heart disease can be a silent disease with many cats showing no outward signs of disease.

Heart disease can affect any cat, although kittens under six months of age are less likely to have a heart-related condition.

The end result of heart diseases is heart failure, which may be left-sided or right-sided, however, in late-stage heart failure, both sides are usually affected.

Congenital heart disease (CHD)

  • These are defects that are present at birth. There are several causes of congenital defects in cats, including genetic, infectious, toxicologic, nutritional, pharmaceutical, environmental. In many cases, the cause will be unknown.

Acquired heart diseases

  • These conditions are not present at birth but develop later and can be primary or secondary. Primary myocardial diseases affect the heart muscle, which results in the heart being unable to function as it should, which can lead to heart failure. Secondary myocardial diseases are due to inflammation of the heart muscle caused by an infection.

Heart diseases can ultimately lead to heart failure, in which the heart is no longer able to do its job effectively enough to meet the body’s needs. It may be left-sided, right-sided or both. As the heart fails, fluid builds up, which is known as congestive heart failure.

Anatomy of the heart

The heart is a hollow, muscular organ that consists of four chambers. The two top chambers are the atria; the bottom chambers are the ventricles. The chambers are separated by valves, known as atrioventricular valves which prevent blood from travelling in the wrong direction. The tricuspid valve is on the right, and the mitral is on the left.


Symptoms can vary depending on the type of heart disease your cat has. In some cases, the cat may be asymptomatic, and heart disease comes to light during a routine health check.

  • Coughing
  • Exercise intolerance
  • Difficulty breathing (rapid breathing, shortness of breath, open-mouthed breathing)
  • Weight loss
  • Decline in appetite
  • Fainting
  • Poor or stunted growth in kittens with congenital heart diseases
  • Heart murmur
  • Restlessness
  • Weakness
  • Swollen belly due to ascites/fluid buildup (congestive heart failure)
  • Cyanosis

Acquired heart diseases

Hypertrophic cardiomyopathy

Feline hypertrophic cardiomyopathy (HCM) is the most common type of heart disease in cats; it occurs when the left ventricular wall becomes excessively thickened. This results in a reduction in the size of the left atrium which means it is unable to accept as much blood, this causes a build-up in the left atrium, lungs, and lining of the chest, resulting in difficulty breathing. This is known as congestive heart failure. Some breeds such as the Maine Coon and Ragdoll have a genetic mutation that can predispose them to heart disease; thankfully there is a test for this mutation.

Restrictive cardiomyopathy

The second most common cardiomyopathy in cats and occurs when fibrous tissue covers the inner lining and muscle of the heart, which impedes its ability to expand and contract as it should.

Dilated cardiomyopathy

A disease in which the muscle of the heart becomes thinner than normal and occurs primarily in middle-aged to older cats. The left ventricle enlarges, and the wall of the heart is weak and flaccid. This impacts the heart’s ability to contract. It was once linked to a deficiency in taurine (an essential amino acid), but cat food manufacturers have added taurine to cat food, so dilated cardiomyopathy is now quite rare.

Heart attack

Also known as myocardial infarction, heart attacks are thankfully rare in cats. They occur when a sudden blockage occurs in one of the arteries supplying oxygen and nutrient-rich blood to the heart, which causes premature death to the affected area of the heart. In cats, this is usually due to a thrombus (blood clot or a hardened plaque of fat). When a blockage occurs, the area of the heart where the blockage occurs is deprived of oxygen, the longer the blockage remains, the more damage occurs to the heart muscle.

Treatment: The goal of treatment is to restore blood flow to the affected area of the heart; medications will be given to dissolve the thrombus.


Feline heartworm disease (FHD) is a parasitic nematode worm that infests the hearts of cats, dogs and other animals. When infected, cats tend to have lower worm burdens than dogs; however, heartworm is still a serious disease in cats. Infection occurs when a mosquito carrying infective heartworm larvae feed on a cat, transmitting the larvae into the cat’s bloodstream. Some cats will have no symptoms; others may develop a cough or difficulty breathing or sudden death. When symptoms do develop, it is usually due to migration of heartworm to the pulmonary arteries or when a worm dies and dislodges, causing a pulmonary embolism.

Treatment: In some cases, treatment may not be carried out as it comes with its risks. When symptoms are present, your veterinarian may decide to treat them. This may include medications to kill the heartworm or surgical removal of the worms. Other medications may be given to reduce inflammation.

Chronic degenerative heart disease

Also known as endocarditis or valval regurgitation, chronic degenerative heart disease (CVD) affects the valves which separate the atria from the ventricles. Age-related degeneration develops over time, resulting in a thickening and nodular formation of the valves which impedes their function, this allows blood to flow backward into the atrium, known as regurgitation. Eventually, the heart enlarges, and fluid leaks out of the heart and into the lungs (pulmonary edema) or the abdomen (ascites). This build-up of fluid is called congestive heart failure.

Treatment: There is no surgery to correct this disease. The goal of treatment medications to remove excess fluid from the body as well as restrict activity and feed a low sodium diet.

Congenital heart diseases

Atrioventricular valve dysplasia (AVD)

This disease occurs due to a defect in either the left (mitral) or right (tricuspid) valve which separates the ventricles from the atrial chambers. These valves may be malformed, abnormally thick or improperly attached. The faulty valve allows blood to leak back into the atria, resulting in blood pooling on the affected side. If the mitral valve is abnormal blood will pool in the lungs, if the tricuspid valve is abnormal, it will pool in the body.

Treatment: There is no surgery to correct this disease. The goal of treatment is to manage the disease with medications to remove excess fluid from the body, restricted activity, low sodium diet.

Patent ductus arteriosus (PDA)

The ductus arteriosus is a blood vessel located within the fetal heart which connects the pulmonary trunk with the aorta and allows blood to bypass the fetal lungs which are filled with fluid until birth. Shortly after birth, the ductus arteriosus should close off, which allows blood flow to the lungs for oxygenation. In some cats, the ductus arteriosus doesn’t close off as it should, which eventually leads to congestive heart failure.

Treatment: Surgical closure of the affected vessel.

Septal defect (hole in the heart)

The most common congenital heart defect to affect cats, a septal defect is an opening in the septum (or wall) that separates the right and left sides of the heart. The most common septal defect is a ventricular septal defect. Most commonly, this hole allows blood to flow from the left to the right-hand side of the heart. The severity of this disease depends on the size of the hole. A small hole (known as restrictive) may cause no problems, however medium and large defects cause an overload of the pulmonary (lung) circulation resulting in left-sided congestive heart failure.

Treatment: Small holes require no treatment; in some cases, they may close as the kitten grows. Medium to large defects may require medical management such as diuretics or ACE inhibitors. Pulmonary arterial banding is a surgical procedure that may be necessary to increase pressure in the right ventricle, which helps to reduce the blood flow from the left ventricle. This procedure isn’t curative but can help relieve symptoms.

Pulmonic stenosis

Stenosis refers to a narrowing of the pulmonary valve, which results in an obstruction of blood flow from the right ventricle to the pulmonary artery. This defect may run concurrently with tricuspid valve dysplasia which makes the condition worse. Not only does the heart have to work harder to pump the blood through the narrowed pulmonary valve, but it also flows backward as a result of the tricuspid valve deformity. This can lead to hypertrophy and dilation of the right ventricle as well as right-sided heart failure.

Treatment: This may vary depending on the severity of the defect. In cats with mild pulmonary stenosis, no treatment may be necessary. More severely affected cats may require balloon catheter dilation (balloon valvuloplasty). This is a procedure where the surgeon inserts and inflates a balloon into the pulmonary valve to break down the obstruction. Other treatment options include beta-blockers and medical management of congestive heart failure.

Tetralogy of Fallot (TOF)

This rare disorder affects four heart defects.

  • Septal defect (hole in the heart)
  • Pulmonic stenosis
  • Right ventricular hypertrophy develops as the heart has to pump harder
  • Dextroposition of the aorta allows blood from both ventricles to enter the aorta

Blood shunts from the right to the left ventricle, bypassing the lungs. This results in cyanosis (blue-tinged skin and gums) due to hypoxia (lack of oxygen). Polycythemia may develop as a result of reduced oxygen levels bringing on additional complications. For a great video explanation of this condition, click here.

Treatment: Medical management of TOF may include periodic phlebotomy with IV fluid replacement (removal of blood) to maintain a packed cell volume below 62%, exercise restriction, beta-blockers to decrease heart rate and right-to-left shunting and palliative surgery. The prognosis is poor.

Endocardial fibroelastosis (EFE)

The endocardium is a thin membrane that lines the inside of the chambers of the heart and the valves. Endocardial fibroelastosis is a heart disease characterised by a thickening of the endocardium due to fibrous and elastic deposits and left ventricular and atrial dilation. Burmese and Siamese cats are at the greatest risk.

Treatment: There is no effective treatment for this condition; supportive care, including oxygen therapy, may be provided.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

    View all posts