Cats can develop many different cardiovascular diseases. The ones discussed below are the most common.
Degenerative Valve Disease
This acquired disease is characterized by a thickening of the heart valves. Degenerative valve disease is uncommon in cats. A veterinarian can often diagnose degenerative valve disease based on physical examination findings and appropriate imaging procedures, which may include chest x-rays and echocardiography (ultrasonography). Affected cats can live for years with appropriate treatment. (For a more detailed discussion of degenerative valve disease, see Heart and Blood Vessel Disorders of Dogs: Degenerative Valve Disease.)
Disorders of the Heart Muscle (Cardiomyopathy)
Cardiomyopathy is the name for any disease that mostly affects the heart muscle. The cardiomyopathies of animals are diseases with no known cause that are not the result of any generalized or primary heart disease. In cats and other animals, they have been classified as dilated cardiomyopathy, hypertrophic cardiomyopathy, and restrictive or unclassified cardiomyopathy. Cardiomyopathy can also occur as a result of other diseases. In these cases, they are usually called secondary myocardial diseases.
Dilated cardiomyopathy is a disease that causes the progressive loss of the heart muscle's ability to contract. The cause is unknown. Several forms of secondary dilated cardiomyopathy exist; for example, one form in cats is caused by a deficiency of taurine, an amino acid. The incidence in cats has decreased dramatically since the discovery in 1985 that taurine deficiency was responsible for most cases. Since then, taurine levels have been increased to acceptable levels in all commercial cat foods. Today, most cases are not taurine responsive and reflect primary disease of unknown cause.
The outlook is grave for cats with dilated cardiomyopathy that is not taurine responsive. Most cats only survive 2 weeks after diagnosis. Cats that have taurine responsive cardiomyopathy also have a high risk of death. However, cats that can be kept alive long enough for taurine supplementation to become effective (2 to 3 weeks) have an excellent outlook.
Hypertrophic cardiomyopathy is a condition in which the walls of the left ventricle thicken and become stiff as a result of a heart muscle disorder. It is the most common primary heart disease diagnosed in cats. It occurs in families in certain breeds of cats such as Maine Coon cats and American Shorthairs. The disease may be seen in cats from 3 months to 17 years of age, although most patients are middle aged. It is more common in males than females. The cause is believed to be an inherited genetic defect. Although this has not been proved in cats, the genetic factor has been documented in humans with this disease.
Affected cats may not have any signs or may have sudden onset of difficulty breathing, collapse, and weakness or paralysis of the hind limbs. A veterinarian may note abnormal heart sounds, including murmurs and gallop heart sounds. Fluid may accumulate in the lungs and in the space between the lungs and the chest wall. Blood clots may form and lodge at the point where the aorta divides near the hips (called saddle thrombi), leading to muscular weakness or paralysis of the hind limbs. X-rays and echocardiography (ultrasonography) may be helpful to diagnose the condition as well as to determine the best treatment.
Treatment is directed at controlling signs of heart failure, improving cardiac function, and reducing the incidence of blood clots. Diuretics (to reduce fluid buildup), oxygen, nitroglycerin, calcium-channel blockers, beta-blockers, or ACE inhibitors may all be considered. Many mildly affected cats have a good longterm outlook; however cats with congestive heart failure have a poorer outlook.
Restrictive cardiomyopathy develops when either one or both ventricles become stiff without significant thickening of the muscle fibers. The cause is not known. The stiff heart muscle fibers cause the ventricles to resist filling with blood between heartbeats. To confirm a diagnosis, cardiac catheterization or echocardiography (ultrasonography) is usually required. Signs and treatment are similar to those for hypertrophic cardiomyopathy (see above); however, the outlook seems to be worse, especially in cats with congestive heart failure.
Unclassified cardiomyopathy is a disease of cats with obvious abnormalities of the heart muscle on echocardiography (ultrasonography) that do not clearly fit into any other category. The cause is not known.
Other Causes of Heart Muscle Failure
A form of cardiomyopathy called atrial standstill destroys the muscle wall of the atrium and occasionally affects the muscle wall of the ventricle. This disease has been reported in some cats with coexisting dilated cardiomyopathy. Treatment is rarely effective.
Endocardial fibroelastosis is a disease of unknown cause that leads to thickening of the lining of the left atrium, left ventricle, and mitral valve. It is a rare cause of heart muscle failure in young cats. Signs, treatment, and outlook are similar to dilated cardiomyopathy (see Heart and Blood Vessel Disorders of Cats: Dilated Cardiomyopathy).
Arrhythmogenic right ventricular cardiomyopathy is a rare cause of heart muscle failure in cats. It is restricted primarily to the right side of the heart, but may also involve the left ventricle. It is characterized by a fibrous and fatty muscle of the right ventricle causing progressive heart muscle failure. Signs include difficulty breathing, increased breathing rate, fainting, and nonspecific signs such as loss of appetite and lethargy. Treatment is similar to that for dilated cardiomyopathy (see Heart and Blood Vessel Disorders of Cats: Dilated Cardiomyopathy).
The endocardium is the thin membrane that lines the heart cavity. Infection of the endocardium typically involves one of the heart valves, although endocarditis of the cavity's wall may occur. Infection is caused by bacteria carried in the blood. The infection gradually destroys the valve and keeps it from working properly. The disease is rare in cats, with the aortic and mitral valves being most commonly affected.
Treatment is directed at controlling signs of congestive heart failure, resolving any significant arrhythmias, killing the bacteria that started the infection, and eliminating the spread of infection (see Heart and Blood Vessel Disorders of Dogs: Infective Endocarditis).
The pericardium is the membrane surrounding the heart. When fluid builds up in the pericardium, pressure on the heart increases. The increased pressure gradually compresses the heart, interfering with its ability to pump blood. This condition is called cardiac tamponade. This compression of the chambers significantly affects blood circulation and causes swollen jugular veins and accumulation of fluid in the abdomen. In addition, too little oxygen reaches the body's tissues. This condition is uncommon in cats, but may be caused by cancer (usually lymphoma in cats), infections (for example, feline infectious peritonitis), injury, chamber rupture, and congestive heart failure.
Cats with cardiac tamponade require urgent treatment. Medical treatment may not be able to rapidly reduce fluid buildup within the membrane surrounding the heart. Pericardiocentesis (inserting a needle through the membrane to withdraw the fluid) is commonly used to remove fluid quickly.
High Blood Pressure (Hypertension)
Systemic hypertension is an increase in the body's blood pressure. There are 2 major types of systemic hypertension. Essential (primary) hypertension, which is of unknown cause, is common in humans but rare in cats. Secondary hypertension results from a specific underlying disease. In cats, the most common causes are kidney disease and hyperthyroidism (overproduction of thyroid hormones).
Cats with extremely high blood pressure may have no signs that are visible to the owner. Blood tests may help with diagnosis of the cause of high blood pressure. Treatment should be started in cats with sustained and severe high blood pressure, or in pets with sustained high blood pressure and an underlying cause such as kidney failure.
Pulmonary hypertension is elevation of blood pressure in the lungs. Possible causes include increased thickness of blood (for example, an abnormal increase in red blood cells) and increased pulmonary blood flow (caused by, for example, a ventricular septal defect, patent ductus arteriosus, or an atrial septal defect). Other causes include abnormalities of the blood vessels in the lungs, which may be caused by heartworm disease, narrowing of the arteries within the lungs, or blood clots within the lungs. Signs are similar to those seen in right-sided congestive heart failure, such as accumulation of fluid in the lungs or abdomen. A swollen and pulsating jugular vein may be noted. Doppler echocardiography (ultrasonography) is the most likely method of confirming the diagnosis. Treatment is usually not effective, and the outlook is poor. The best chance for a successful outcome is the identification and treatment of the underlying disease.
Last full review/revision July 2011 by Davin Borde, DVM, DACVIM; Jorge Guerrero, DVM, PhD, DEVPC (Ret); Michelle Wall, DVM, DACVIM; Clay A. Calvert, DVM, DACVIM; Benjamin J. Darien, DVM, MS, DACVIM