Heart Disease

ventricular septal defect (vsd) | atrioventricular valve dysplasia | patent ductus arteriosus (pda) | endocardial fibroelastosis | aortic stenosis | pulmonic stenosis | other congenital heart defects | primary (idiopathic) cardiomyopathies | secondary cardiomyopathies | valvular disease | pericardial disease

Introduction: The heart is an extremely complex organ upon which the life of any animal depends from minute to minute. It is responsible for providing the power to circulate blood throughout the body.

Heart problems are relatively common in feline patients seen at veterinary hospitals. Most cats with heart problems are 7 years and older. Some heart diseases, however, are more common in younger cats. Heart disease in cats can be very complicated and must be treated on an individual basis. Therefore, this section will give only a brief overview of some of the more common heart disorders seen in cats. The intent of this material is to give the pet owner a better understanding of the clinical signs, diagnosis, and treatment for many of the problems associated with the feline heart.

Common Terms:

  1. Cardiac - Adjective referring to the heart.
  2. Artery - A blood vessel carrying blood away from the heart.
  3. Vein - A blood vessel carrying blood toward the heart.
  4. Capillary - Tiny vessel from which oxygen and nutrients dissolve out of the blood stream and into the surrounding tissue. Capillaries are present everywhere in the body and are the connection between arteries and veins.
  5. Atrium - Upper chambers in the heart. Cats have two atria, right and left.
  6. Ventricle - Lower chambers in the heart. Cats have two ventricles, right and left.
  7. Valve - "Doorways" into and out of the ventricles. Each ventricle has two valves, one for inflow and one for outflow. Subsequently, each feline heart has four valves. The valves which allow blood to flow into the ventricles open during the first phase of a heartbeat and close during the second phase. The valves which allow blood to flow out of the ventricles function in the opposite manner, closing during the first phase of the heartbeat and opening during the second phase. The four feline heart valves are described as follows:

The "lub-DUB, lub-DUB" sound heard when listening to the heart with a stethoscope is actually the noise made when the valves shut and create turbulence in the blood. The pulmonic and aortic valves close on the "lub" portion of the sound, while the right and left atrioventricular valves close on the "DUB" portion of the sound.

  1. Aorta - The largest artery in the body. The aorta carries blood from the left ventricle down through the chest and into the abdomen. Arteries branch off the aorta carrying blood to all parts of the body.
  2. Pulmonic artery - The major vessel which carries blood from the right ventricle into the lungs to receive oxygen. The pulmonic artery and its branches are the only arteries in the body that normally carry blood which is low in oxygen content.
  3. Vena cava - The largest veins in the body. All veins eventually empty into one of these two veins. One carries blood from the head and upper body into the heart, and the other carries blood from the lower body. Both empty into the right atrium.
  4. Pulmonic veins - Veins which drain blood from the lungs back into the heart. The pulmonic veins empty into the left atrium and are the only veins in the body which carry blood high in oxygen content.
  5. Systole - Contraction or pumping phase of the heartbeat. During systole, the heart contracts and empties its chambers, pumping blood into the body.
  6. Diastole - Resting or filling phase of the heartbeat that occurs in between heartbeats. During this brief resting phase, the heart fills with blood.
  7. Murmur - An abnormal heart sound heard with a stethoscope. Murmurs may be caused by turbulent blood flowing through a defect in the heart or through a faulty valve that is not closing when it should.
  8. Arrhythmia - An abnormality in the electrical activity of the heart. Some types of arrhythmias can be life-threatening emergencies.
  9. Edema - Fluid buildup in the tissues. Edema may be due to various causes; heart defects are one of the more serious causes in which edema may severely affect the health of the animal.

Heart Disease

A large variety of problems can lead to heart disease. Deaths stemming from a heart disorder are usually due to either the development of a fatal arrhythmia or to congestive heart failure and its various complications. All heart problems can be placed into one of two categories: congenital or acquired. A few of the more common heart diseases will be addressed as follows:

Congenital - These are defects present from birth. Congenital cardiac defects are among the most common defects that occur in kittens. This is probably due to the complicated process of cardiac development in the unborn fetus.

  1. Ventricular Septal Defect (VSD) - This is the most common congenital defect found in cats. A VSD is a defect in the heart wall (septum) that separates the left and right ventricles. This defect is a hole that allows blood to pass abnormally from the one ventricle to the other (usually left-to-right). This flowing of blood from the left to the right ventricle causes overload of the heart with blood. A severely overloaded heart eventually begins to fail and allows blood to back up into the lungs and other tissues of the body. Edema is commonly the result and is one of the classic symptoms of heart failure. Edema in the lungs can result in coughing, while edema of the tissues results in swelling and tenderness. Occasionally, the pressures inside the heart with a VSD will change and allow blood to begin flowing in the opposite direction. This results in a situation known as "Eisenmengerís physiology." Eisenmengerís physiology is where the blood shifts from the usual left-to-right shunt and flows from right-to-left. A right-to-left shunt results in overload of the left side of the heart as well as mixing of oxygen-poor blood with oxygen-rich blood. A cat with this condition may have blue (cyanotic) gums due to a lack of oxygen in the blood stream.

* A similar defect can be found in the wall (septum) that separates the left and right atria. This defect is called an atrial septal defect (ASD) and is not as common as VSDs in small animals.

  1. Atrioventricular Valve Dysplasia - These are mitral and tricuspid valve defects that occur during the developmental stages of the valves. The exact cause for the development of these defects is not known. The faulty valves can be too short, thickened, misaligned, or rolled. The muscles and chordae tendineae (strong cords which hold the valves in place) that control the function of the valves can also be defective. Some cats with this disease can live normally for years without significant problems, while others may quickly deteriorate.
  1. Patent Ductus Arteriosus (PDA) - This is a shunt or duct, normally present in unborn kittens, which allows blood to pass from the right side of the heart to the left. This shunt (ductus arteriosus) is located just above the heart and is a connection between the two main arteries leading away from the heart, the pulmonic artery and the aorta. The ductus arteriosus allows blood to bypass the undeveloped lungs and enter directly into the aorta. The ductus arteriosus normally closes within hours to days after a kitten is born and starts to breathe on its own. If the ductus arteriosus fails to close, blood is still shunted through, although the direction usually reverses itself and shunts blood from the aorta into the pulmonary artery. This is called a left-to-right shunting PDA. This condition results in overload to the left side of the heart, and many affected kittens will succumb to heart failure within a year without surgical treatment.
  1. Endocardial Fibroelastosis - This is a condition where the inner lining (endocardium) of the heart is thickened. It most commonly occurs in Siamese and Burmese cats, and the disease can be genetically passed from parent to offspring.
  1. Aortic Stenosis - This defect consists of a ring of thickened tissue (a constriction) around or near the aortic valve where blood flows from the left ventricle into the aorta and rest of the body. This ring of tissue makes it very difficult for the heart to pump blood out into the aorta. Blood pressure builds up in the left ventricle, and the heart begins to overwork itself to perform its normal function.
  1. Pulmonic Stenosis - This is usually a defective pulmonic valve. This condition, which is present at birth, includes any defect in the heart which makes it difficult for blood to exit the right ventricle and enter the pulmonary artery and lungs. Because of the defect, blood pressure increases in the right side of the heart and in the vessels that empty blood from the body back to the heart.
  1. Other Congenital Heart Defects: These include persistent right aortic arch, atrial malformations, and Tetralogy of Fallot. Each of these conditions usually can occur and lead to failure of the heart muscle in diseased individuals. Professional advice should be sought when dealing with any congenital defect of the heart.


Acquired Disorders: These are disorders which are not present at birth, but develop at some point later in life. These diseases are broken down into four major categories: primary (idiopathic) cardiomyopathies, secondary cardiomyopathies, valvular disease, and pericardial disease. The term "idiopathic" means that there is no known cause for these diseases of the heart.

  1. Primary (idiopathic) Cardiomyopathies:
  1. Hypertrophic cardiomyopathy is the most common acquired heart disease in cats. This disease results in thickening (hypertrophy) of the left ventricular heart wall. This can obstruct the flow of blood out of the heart, elevate blood pressure in the atria, and cause congestive heart failure. This problem has been associated with high blood pressure and hyperthyroidism in cats.
  • Clinical Signs: These signs include collapse, fainting spells (syncope), difficulty breathing, coughing, an increased heart rate, and a lack of energy. In some cats, blood clots may form in the heart and be spread to various parts of the body. A common area for this problem to occur is the arteries which go to the hind legs. Clots that lodge in these arteries cause paralysis of the hind legs.

  • Diagnosis: A heart murmur is often heard and X-rays (radiographs) show enlarged atria and a "valentine shaped" heart. An echocardiogram (ECG) is also essential in identifying this disease.

  • Treatment: Treatment should focus on reducing the respiratory problems by using drugs that reduce the amount of fluid in and around the lungs. Other drugs should be used to reduce the heart rate and the amount of force the heart expends during its contraction. Aspirin may be used to help prevent blood clot formation. If associated with hyperthyroidism, proper therapy for the overactive thyroid gland may reverse the cardiomyopathy.
  1. Dilated Cardiomyopathy is a second type of primary cardiomyopathy disease. It is found more commonly in dogs, but it does occur in cats. This disease results in dilation of the heart, possible thinning of the ventricular heart wall, and dysfunction of the heart during contraction. This irritation to the heart muscle can lead to rhythm abnormalities (atrial fibrillation) and congestive heart failure. It is thought that this problem in cats is associated with taurine deficiency in the diet. This is one reason why taurine is an essential amino acid for cats.
  • Clinical Signs: Signs of this disease include weight loss, collapse, fainting spells (syncope), difficulty breathing, coughing, increased heart rate, fluid accumulation (edema), and hind limb paralysis from blood clot formation.

  • Diagnosis: A heart murmur is often heard with a stethoscope and X-rays (radiographs) show an enlarged heart and left atrium. An echocardiogram is the best technique for identifying this disease.

  • Treatment: Treatment should focus on reducing the respiratory signs by using drugs that reduce the amount of fluid in and around the lungs. Other drugs should be used to maintain a regular heart rhythm and prevent ventricular tachycardia (ventricles beating too fast). Aspirin can be used to help prevent blood clot formation.
  1. Restrictive cardiomyopathy is the least common of the three primary cardiomyopathies. This disease can cause many different signs including vomiting, difficulty breathing, and fluid accumulation. The diagnosis and treatment is similar to hypertrophic cardiomyopathy.
  1. Secondary Cardiomyopathies: Following is a list of the most common causes of secondary cardiomyopathy in small animals:
  1. Endocrine (hormone related) - hyperthyroidism, excessive growth hormone secretion
  2. Genetic - atrioventricular myopathy
  3. Infiltrative (invasive) - neoplasia
  4. Inflammatory - viral, fungal, bacterial, or protozoal infections
  5. Lack of blood flow (ischemia) - blood clots (thromboembolism)
  6. Nutritional - taurine and L-carnitine deficiency
  7. Pressure or volume overload on the heart - high blood pressure (hypertension) and valve problems
  8. Toxic - rattlesnake venom and doxorubicin (chemotherapeutic drug)

*The diagnosis and treatment for each of the above causes of secondary cardiomyopathy will be different depending on the cause. In general, the symptoms affecting the cat will need to be treated and the cause of the condition will need to be eliminated if possible.

  1. Valvular Disease:
  1. Infective Endocarditis - This is an infection of the heart muscle, valves, or supporting structures of the heart. Bacteria are usually responsible for the infection, although fungal infections can also occur. The bacteria must first enter the bloodstream and be carried to the heart. Because the bloodstream carries bacteria to all parts of the body, organs other than the heart (particularly the kidneys and the spleen) may also be affected. The source of bacteria entering the bloodstream differs from individual to individual; however, the most common sources are the mouth, skin, digestive tract, and urinary tract. Cats with bad teeth, urinary tract infections, ear and skin infections, or that will eat anything, including garbage, are more at risk.

    The heart valves and supporting structures seem to be the more common sites of infection within the heart, possibly due to their constant exposure to turbulent blood. Any of the four heart valves may be affected. Valves on the left side of the heart (aortic and mitral valves) are affected more often than the valves on the right side of the heart.
  • Clinical Signs: Heart murmurs (especially a new heart murmur never previously heard), fever, and sometimes lameness are found in cats with infective endocarditis. Other clinical signs will vary and depend upon where in the heart the infection has occurred and what other organ systems are involved.

  • Diagnosis: Blood cultures are an important part of making the diagnosis of infective endocarditis. This diagnostic test requires that blood samples be taken and sent to a diagnostic laboratory for culture. The culture results may take up to 3 weeks to be finalized; therefore, treatment is usually started before a final test result can be obtained. If bacteria are found circulating in the bloodstream, and recent heart problems are present, a positive (definitive) diagnosis of infective endocarditis can be made. If the actual bacterial colony is large enough, it may be viewed with echocardiography (ultrasound of the heart). Radiographs (X-rays) of the heart, CBC, blood (serum) chemistry panel, and ECG are other recommended tests to aid in diagnosis. See Section D for additional information on the above tests.

  • Treatment: Therapy for infective endocarditis focuses on antibiotics and heart stabilization. Based on their general success in helping patients with this condition, antibiotics are chosen in the beginning before blood culture results can be finalized. After obtaining blood culture results, a veterinarian will select antibiotics based on the culture and sensitivity data (please see Culture and Sensitivity page D135). Treatment for damage done to the heart itself is based on severity, structures affected, and need.

  • Prevention: Maintaining a healthy pet is critical in preventing this disease. While nothing will guarantee 100% prevention, providing basic pet hygiene is perhaps the most important part an owner can take in avoiding this ailment. Brushing a catís teeth regularly and providing annual dental cleaning under the care of a veterinarian are central in pet hygiene. Keeping a close watch for skin and ear infections, anal gland impactions, urine abnormalities, and strictly monitoring diet are also important components of pet hygiene. Each of these areas is given special attention in other sections of this manual.
  1. Pericardial Disease:
  1. Pericardial effusion - This is fluid that accumulates around the heart in the "heart sac" (pericardium). This fluid can accumulate because of low protein levels, heart failure, certain cancers, bacterial infections, viral infections, or fungal infections. In cats this fluid can also accumulate because of feline infectious peritonitis and toxoplasmosis infections. If the fluid accumulates rapidly, a situation called "cardiac tamponade" can result. Cardiac tamponade, a life threatening problem, is a sudden compression of the heart from rapid fluid accumulation in the pericardium.
  • Clinical signs: Common problems include difficulty breathing, weakness, lack of energy, collapse, and distension of the abdomen. In cases of cardiac tamponade, the cat will have a weak, rapid pulse, distended veins, and diminished heart sounds when listened to with a stethoscope.

  • Diagnosis: Rhythm abnormalities are common and the heart can appear round in shape and enlarged when observed using a radiograph. The most accurate way of diagnosing this problem is by echocardiography.

  • Treatment: In severe cases the fluid must be removed by performing a procedure called a pericardiocentesis. This is where a sterile catheter is used to cleanly enter the pericardium and remove the fluid. The cause for the fluid build-up must be identified and then treated. Depending on the cause, treatment may include antibiotics, antifungals, fluid reducing drugs, anti-cancer agents, plus others.
  1. Other Diseases - Myocardial infarction (MI), or "heart attacks," are commonly blamed for sudden death in cats. True MI in cats, however, is relatively rare. In MI, an object known as an embolus lodges itself into one of the coronary arteries and deprives the heart muscle, fed by that artery, of its blood supply. When deprived of its blood supply and oxygen, the heart muscle will die. If only a small section of muscle is affected, the heart attack is considered minor. A massive heart attack is usually caused by blockage of a major artery or many arteries, and results in the death of a large portion of the heart. The embolus is usually in the form of a blood clot, but can also be a fragment of dislodged tissue, a foreign object, or an air bubble. Embolus damage in cats can also affect other organs such as the lungs or the kidneys.
This is an electrocardiogram (ECG or EKG) machine. This machine is used to determine if a heart condition is causing any abnormalities in the heartís electrical rhythm. It is used to help diagnose specific arrhythmias of the heart.