The heart is a muscular organ located in the thorax of the cat. It, along with the arteries which carry blood away from the heart and the veins which carry blood back to the heart, comprise the cardiovascular system. The heart itself serves as the pump to move blood to and from as described above. In general, this system carries oxygen and nutrients to the tissues of the body and carbon dioxide and wastes so that they can be excreted from the body. This system also transports hormones to the body and helps maintain body temperature.

The heart pumps blood to the lungs each time it beats. There, carbon dioxide is released and the blood absorbs oxygen. Once oxygenated, the blood returns to the heart where it is ready to be pumped to the tissues of the body. To supply itself with blood, the heart has its own circulation system called the coronary arteries and veins. As mentioned, the heart is a muscle, but it has a unique system of nerves to control its contractions and valves to direct blood flow. Interruption of any of these components can lead to cardiac disease.

Diseases of the heart are common in the cat. While cats infrequently suffer from heart attacks like humans, cardiomyopathy, arrhythmias and congestive heart disease is commonly seen in pet cats.

When nerve conduction is altered in the heart and causes the rate and rhythm of the heart to vary from normal, an arrhythmia occurs. Some arrhythmias may be mild and go undetected while others can lead to heart failure and death if not properly treated. Nodes within the heart act like electrical pacemakers, directing and regulating how the heart beats. Stimuli produced by these nodes are carried to the muscular tissue by their own small nerves, but it is important to understand that the central nervous system, chemicals in the blood and hormones can affect this automatic function.

Arrhythmias may be caused by infections of the heart, congenital heart defects, diseases of the heart muscle, trauma, neoplasia of the cardiovascular system, neurologic disorders, endocrine disease, infections elsewhere in the body, digestive system disease, electrolyte disturbances, drugs, toxins and other external insults. With so many possible causes, cardiac arrhythmias are a challenge for your veterinarian to diagnose and treat. Clinical signs of arrhythmia may be nonexistent or so mild as to be easily overlooked. Cats with symptoms will exhibit weakness which may seem to come and go, inability to perform routine levels of exercise, collapse or fainting spells (syncope), trouble breathing or coughing and possibly a swelling of the abdomen. Some cats may die without warning or any hints of illness!

Other types of cardiovascular disease may mimic the signs of arrhythmia and as other diseases may produce heart dysfunction, a thorough diagnosis is very important. A thorough history, the clinical signs, chest X-ray, EKG analysis, blood, serum and urine testing and cardiac ultrasound are often all needed to properly diagnose the cause of an arrhythmia. 

There are many different types of arrhythmia, a description of which is far beyond the scope of this program. Several simplified groupings are available:

Bradyarrhythmias occur when some part of the heart rate becomes slower than normal. Tachyarrhythmias occur when some part of the heart rate is faster than it should be and Conduction Disturbances include a variety of irregularities consistent with grossly altered conduction of nerve impulses within the heart. It is important to note that all these disturbances can lead to cardiac arrest and sudden death unless CPR and other appropriate measures are taken to save the cat.

Treatment of this problem is no simple task. A most exacting diagnosis is critically important so that the cause can be addressed directly and not by trial and error. If secondary conditions are present, these should be addressed first, as often the arrhythmia will disappear as this other problem becomes resolved or controlled.

There is no one exact medication to treat each and every arrhythmia as each is unique in nature and similar dysfunction will often produce variable degrees of clinical illness. Your veterinarian will best be able to select appropriate medications: There are a wide variety of possible drugs that can be utilized. Some of these include the following: digitalis, furosemide, captopril, hydralazine, lidocaine, propranolol, atropine and theophylline. The appropriate combinations will have to be carefully individualized for each cat and regular follow-up exams, EKG analysis and blood testing will be important to keep control of the condition.

Infections in other parts of the body often enter the blood stream and as all blood eventually passes through the heart, these bacteria can become deposited on the valves and lining tissues of the heart and begin an infection there. Valves become damaged and begin to leak blood and ultimately congestive heart failure can result. In general, however, this form of heart disease is uncommon in the cat. ((Endocarditis))

Infections of the uterus, dental infections, skin infections, pneumonia and infections after medical or surgical care can all lead to this endocarditis. The clinical signs can mimic other conditions and include fever, weakness, heart murmur, vomiting, poor appetite, lameness and congestive heart failure signs. A few cats may become ill and die of heart failure in a short period of time. Diagnosis is based on history or suspicion of infection, clinical signs, blood cultures, X-rays, blood counts and serum chemical analysis. EKG and ultrasound analysis may also be helpful in establishing the diagnosis.

If proper diagnosis and culture of the attacking organisms is made, then general antibiotic therapy specific for the organism should be effective. The after effects of the infection such as arrhythmia or congestive heart failure may, however, require additional and ongoing therapy.

Heart failure occurs when or as the heart is unable to properly circulate blood throughout the body and as the heart becomes unable to meet increased demand placed upon it during exercise. The causes of congestive heart disease are numerous as most any condition that damages the heart or part of the heart in some way will ultimately produce this disease. These include valvular diseases, cardiomyopathy, congenital diseases/defects, arrhythmia, heartworm disease, pericardial diseases and cardiac neoplasia. Diseases of the respiratory system can also produce failure of the heart.

The heart is divided into two sides. The right side is responsible for receiving blood from the body and pumping it to the lungs; the left side is responsible for receiving blood from the lungs and pumping it back through the tissues of the body. The clinical symptoms of heart disease will vary depending on which side of the heart is dysfunctional. (both sides can be affected)

Right-sided heart failure will generally produce clinical signs that include weakness, fainting, inability to exercise, enlargement of abdominal organs and possibly the collection of fluid within the abdomen (ascites), distention of the veins and swelling to the feet and lower legs. These symptoms occur as venous blood cannot flow back to the heart readily and "pools" in the extremities and abdominal cavity. ((Ascites))

Left-sided heart failure with often produce signs of weakness, fainting, decreased urination, coughing, difficulty breathing, sometimes rapid breathing and possibly a blue or purple discoloration to the gums and tongue (cyanosis). Some cats may find it difficult to get comfortable and lie still. These symptoms occur as fluid builds up in the lung tissues causing pulmonary edema.

Cats with Generalized heart failure (both sides) will then often exhibit some combination of the symptoms noted above. Generalized and non-specific signs of these conditions may also manifest including weight loss, poor appetite and loss of muscle mass and condition. Diagnosis is based on physical exam, history of the symptoms, X-rays, ultrasonography, blood counts and serum chemistries, EKG analysis and blood pressure measurements.

While it should be understood that most all cases of heart failure result in death of the cat (not many heart transplants are given to felines each year), many patients can live for years and have a high quality of life with proper treatment and monitoring. Unless treating a specific underlying condition such as a bacterial endocarditis, most therapy centers on controlling the symptoms or problems produced as the heart fails.

Many patients are given a diuretic such as furosemide to help remove fluid from the lungs and organs. Drugs such as nitroglycerin or hydralazine are used to dilate blood vessels and decrease the pressure against which the heart must pump. Drugs such as Captopril or Enalapril also are used to dilate blood vessels and remove fluids and are sometimes used in combination with the aforementioned agents.

Digitalis is often employed in more chronic cases of heart failure or as the overall condition of the cat worsens. This drug improves the strength with which the heart pumps and tends to slow the heart to a more regular beat. It can be used with other medications, but it must be carefully administered to avoid toxic side effects. Oxygen therapy may be given to some cats and low sodium diets are available to further limit fluid accumulation.

Overall, the best combination and dosage of drugs used for every cat will vary with the length and severity of the disease and the response of the cat to the therapy. Most cats with advanced heart failure will be unable to exercise at a normal level. The stresses that exercise places on the heart should be clearly understood and thusly limited by the owner.

The long-term prognosis for each patient, irrespective of those with rapidly progressive disease, can be enhanced by regular follow-up care with the veterinarian. Blood tests to monitor serum electrolytes and detect early evidence of drug toxicities or organ failure, repeated X-rays or EKG's to access heart function and general physical examinations all help cats with this disease live longer, happier lives. Again, it must be understood that at some point, the degree of heart failure may become too advanced, or general organ failure may ultimately overtake even the best of patients.

Cardiomyopathy is a serious and often fatal dysfunction of the heart muscle that produces abnormal contractility of the heart and altered pumping of blood. Three forms of cardiomyopathy are commonly recognized:

Dilated Cardiomyopathy was the most common version of the disorder until it was discovered that a deficiency in taurine was the primary cause in cats. Since that time, dietary supplementation has decreased the incidence of the condition significantly. In these cases the left ventricle of the heart becomes grossly distended/dilated and congestive heart failure ensues. ((Dilated Cardiomyopathy))

Hypertrophic Cardiomyopathy describes an abnormal thickening of the muscle of the left ventricle of the heart. The exact cause of this condition is unknown although a genetic cause is suspected. Young to middle-aged cats seem most at risk for developing this disease. As the thickened wall inhibits the proper pumping of blood, congestive heart failure and thromboembolism commonly occur in these cats. ((Hypertrophic Cardiomyopathy))

Restrictive Cardiomyopathy, also known as Intermediate Cardiomyopathy, is a third form of the disease although opinion varies as to the prevalence and certainty of the cardiac changes present. While debate continues as to what pathology exactly must be present to make this diagnosis, some consensus has it that a decrease in size of the left ventricle caused by heavy fibrosis of connective bands within the heart will be present. Combined with other abnormalities additionally possible, the condition results in poor pumping action by the heart. The cause of this condition is also unknown.

Clinical signs in general for cats with cardiomyopathy include weakness, poor appetite, weight loss, rapid labored breathing, coughing, swelling to the abdomen or extremities, fainting episodes, hindleg pain and/or paralysis and sudden death. Some cats may display no symptoms before a sudden and often severe onset of the disease. This condition will appear similar to many other diseases of the heart. Diagnosis is based on history, physical examination, EKG testing, X-rays, echocardiograms, complete blood and urine testing along with thyroid function testing.

Treatment for most cats is partially similar to that of congestive heart failure and the extent of treatment will depend on the severity of the disease and the associated clinical signs. Most cats will need rest and avoidance of any stressful activity. A low sodium diet is also important. Digitalis, diuretics such as furosemide and other drugs are all employed. Careful monitoring of the patient and organ function tests and EKG analysis are required to monitor the status of the patient as time goes by. Cats with dilated cardiomyopathy may have a slightly better survival rate than cats with the hypertrophic form. Overall, however, the prognosis for long-term survival is at best fair.

Myocarditis denotes inflammation of the heart muscle, vessels and lining tissues of the heart. As every drop of blood must pass through the heart, the organ is highly susceptible to attack. Myocarditis can be caused directly by infectious organisms such as bacteria and toxoplasmosis, or secondary to other diseases such as hyperthyroidism, kidney disease, potassium disturbances, toxins and chemicals including drugs, taurine deficiency and lymphosarcoma.

Insult of the heart muscle can lead to arrhythmia and congestive heart failure. Most commonly, however, myocarditis is tied to cardiomyopathy, the most common and significant heart problem of the cat. If infection of the heart is occurring, the condition will most often come on suddenly, accompanied by fever, lethargy, weakness, coughing and trouble breathing with other symptoms related to the disease or condition that lead to the inflammation of the heart. When the condition is secondary to other diseases, the cardiac disruption needs to be viewed in relation to that disease process and correction thereof will often lead to improvement in heart function.

Diagnosis is based on all the clinical signs, X-rays, EKG testing, blood counts, serum chemical analysis, urinalysis and any testing specific to other diseases which may effect the heart. Diagnosis is difficult and cooperation with your veterinarian will provide the best opportunity to spot the primary cause and render treatment that will allow the heart muscle and related tissues to heal. Treatment is, therefore, specific for the condition that actually damaged the heart and to complications left afterwards.

The pericardium is a thin sac that surrounds the heart as it sits inside the chest. The most common conditions of this tissue relate to some type of fluid building up inside the sac and restricting the normal movement (beating) of the heart muscle. On occasion scar tissue may form and limit heart motion. The build-up of fluid is called Pericardial Effusion and this is the most common pericardial problem seen. Pericardial effusions are usually secondary to other conditions including cardiomyopathy, FIP, bacterial infections, lymphosarcoma and in some cases for no apparent reason.

When effusions restrict heart activity, the term Tamponade is used; when fibrous tissue (scar tissue) causes the restriction it is termed Constrictive Pericarditis. These conditions are all rare. Clinical symptoms include lethargy and weakness, troubled breathing, cough, fluid collecting in the abdomen (ascites), fainting and even sudden death. Diagnosis is accomplished through physical examination, EKG analysis, X-rays and echocardiography. Blood counts, serum chemistry and other specialized tests may be needed to diagnose the primary cause of the disease.

As with other cardiac conditions, careful identification and treatment of any primary condition is essential. Antibiotics would be useful to treat a bacterial infection. Placing a needle in between the pericardium and the heart to drain off any fluid is always indicated. Many cases can be cured after 1 or 2 treatments. In some cases, surgical removal of part of the pericardium to provide permanent drainage will be required. This involves opening the chest and doing surgery around the heart and lungs. This treatment is also effective for restrictive pericarditis.

Feline heartworm disease is a heart and circulatory disorder caused by the worm parasite Dirofilaria immitis. This parasite is recognized worldwide, a common problem for domestic dogs with the cat generally being infested at a lower rate. These worms exist in the heart and large blood vessels of the cat (and dog) and reproduce by releasing tiny immature larvae into the blood stream. The larvae are called microfliaria and may remain in the blood for years. Most cats will have only 3-6 adult worms in the heart at any one time. ((Heartworm Cycle))

When a mosquito bites an infected dog (usually it is the dog that is the source of infection for the cat) and ingests blood, some of these microfilaria are also ingested. Once inside the mosquito, the larvae develop into infective larvae and after this, when the mosquito bites a cat, some of these larvae will pass into and under the skin of that cat. Once inside the cat, these larvae develop further and migrate towards the circulatory system through body tissues. Finally, after about 6 months, they reach the heart and pulmonary blood vessels where they "settle in" and as adults, repeat the life cycle with some adult worms living for up to 3 years inside the heart. It is these adult worms that cause the damage associated with actually having heartworm disease. ((Heartworms)) ((Heartworms in the Heart)) ((Map of Heartworm Areas))

The presence of the worms can damage the blood vessels that lead from the heart to the lungs (pulmonary circulation), the heart muscle and the internal heart valves. Blood flow is then restricted and the heart must work harder to pump leading to heart disease including congestive heart failure. It is also not uncommon for pieces of worms or blood clots to damage lung tissues as well. Some cats will develop pulmonary infiltrates of eosinophilia. Other complications of this disease include thromboembolism, neurologic disease and pleural effusions.

Clinical signs, it should be noted, often occur months or years after infestation, so regular testing and prevention is more important than waiting for trouble to begin. Clinical signs include coughing, trouble breathing, fatigue, weakness, weight loss and vomiting. Cats seem much more likely than dogs to develop acute and severe symptoms and unexpectedly die due to this illness. Diagnosis is based on physical examination, chest and abdominal X-ray, echocardiography, EKG testing, blood counts and heartworm tests which can detect the disease from/in blood.

Prevention of heartworm disease is important in most areas. Cats should all have an annual blood test to detect the presence of any worms and if not infected, a monthly pill can prevent the disease from ever becoming established in your cat.

Treatment is of concern, as killing the worms too quickly can produce massive thromboembolism (clots) in the lungs and kill the cat. After a thorough evaluation, most cats are hospitalized and placed on intravenous fluids; then 4 injections of an arsenic-containing drug are given over a 2-day period. Other medications may be used to minimize side effects of killing the worms including cortisone to combat allergic-type reactions.

If the patient does well, a few weeks later treatment is also given to eradicate any microfilaria, which still inhabit the bloodstream. A new treatment, using the drug melarsomine is now on the market for dog, which promises to increase the level of safety of treatment and still effectively kill the heartworms. It is not known if this drug will be safe for the cat. Toxicity is a concern for cats treated with thiacetarsamide. Some references advise direct intracardiac removal of the worms, which in most cases will require the help of a specialist to perform such a procedure.

Thromboembolism involves clots that break free from where they form in the heart, aorta or other great vessels and then lodge in smaller vessels causing severe circulatory restriction. The most common presentation of this occurs when a clot blocks the aorta at the point where it divides and provides blood to the hindlegs. Usually this occurs in cats with cardiomyopathy, but cases secondary to congestive heart failure, bacterial endocarditis, tumors of the heart and congenital heart defects do occur. ((Saddle Thrombus))

Symptoms include a very sudden onset of pain (often severe pain) to the limbs or sometimes other locations, weakness, limb paralysis, fainting, coolness to an area, difficulty breathing and possibly neurologic signs if the clot affects some area of the brain or nervous system. Sudden death in some cases can occur. Diagnosis is difficult and can be based on clinical signs, physical examination, history of trauma or heart disease, blood counts and serum chemistries, X-rays, dye studies, ultrasound testing and a neurological evaluation if needed. Unfortunately, sophisticated testing needed to accurately diagnose this problem is sometimes unavailable.

Caught and diagnosed early, thromboembolism can be treated with blood-thinning drugs, drugs to dilate the blood vessels, IV fluids to maintain circulation and medications to control pain. New fibrinolytic drugs can be used in some cases to dissolve clots. Long term care in cats deemed susceptible to having embolism problems include the use of aspirin, coumadin or heparin to deter blood clotting. Surgical removal of aortic clots has been performed but is currently not advised. Treatment of predisposing heart disease is also a top priority. Careful and regular monitoring of these patients will be required.

In the unborn animal, there is an interconnection between the pulmonary artery and the aorta near the heart. This allows blood to bypass the normal flow through the lungs, as the lungs are not needed nor used by the fetus. After the cat is born, this connection will, in most all cases, close down in a few days or weeks with all blood pumping through the lungs to be oxygenated. On occasion this does not happen and a patent ductus arteriosus is then said to be present.

This defect is considered to be hereditary, so cats with the condition should not be bred. When the defect is present after birth, blood to be pumped to the body flows backward into the pulmonary circulation and blood to be pumped to the lungs (unoxygenated) can flow towards the body circulation. ((PDA))

Clinical signs include a very loud and machine-like murmur heard on auscultation of the chest by the veterinarian, cough, blue gums and tongue (cyanosis), rear leg weakness and ultimately death. Many cats can live a few years with the defect as long as stress and the amount of exercise is kept to a minimum. Diagnosis is based on these physical findings, EKG analysis, X-rays and on occasion special X-rays where dye is run through the heart while taking the X-rays.

If caught early and no decompensation of heart function has/is occurred, then surgical ligation (meaning to tie off) of the patent ductus will produce a complete cure and the cat can have a normal lifespan. Without treatment, most cats die before the age of 4. This does, however, mean that the pet will undergo open-heart surgery.

Right aortic arch is a rare abnormality where the aorta and pulmonary arteries form on the side opposite from where they normally form, with the ductus arteriosum (as in patent ductus arteriosus) acting like a rubber band, trapping the esophagus and blocking the flow of food from the mouth to the stomach. The condition is quite rare. ((PRAA))

Kittens usually do well until they begin to eat solid foods, at which time the main symptom is regurgitation of food almost as soon as it is swallowed. Most cats have a great appetite and want to eat, but are thin, as they are unable to ingest any food. Some cats may aspirate (breathe in) the vomit and suffer from aspiration pneumonia which certainly complicates this situation. Diagnosis is based on the history, clinical signs and having the cat eat food laced with barium and taking X-rays to elucidate the blockage.

Properly diagnosed early in select patients, this problem is correctable with surgical ligation and separation of the remnant of the ductus arteriosus, thus freeing the esophagus from its constriction. These patients will generally not survive without this type of surgery. This would require opening the chest and performing surgery around the heart.

Various types of heart defects may be diagnosed, in young kittens primarily. Valvular defects include Aortic Stenosis, Pulmonary Stenosis, Mitral Dysplasia and Tricuspid Dysplasia; stenosis involves a narrowing of the specific valve, a restriction of blood flow and backward pressure within the heart. Valves with dysplasia usually are not completely developed and blood leaks backward in the system. Septal defects involve a hole or opening between chambers of the heart where no such opening should exist. These include Atrial Septal Defect and Ventricular Septal Defect. Patent ductus arteriosus is another common heart defect. Combinations of various defects can also occur.

In early cases, no clinical signs may exist, with an unusual murmur being noted by the doctor upon physical examination. Allowed to persist, most result in congestive heart failure with the clinical signs matching the side(s) of the heart that is failing. Diagnosis is based on ultrasonography and clinical signs, or necropsy if the animal does not survive. Usually no treatment is undertaken as open-heart surgery, rarely done in cats, would be needed.

Shock is mentioned many times throughout this program, as there are many conditions that can cause shock. By definition, shock is a failure of the general circulation; that is, the flow of blood becomes decreased far below what is optimal for life. It is not one disease or simple process, but rather, a complex, multifaceted and dynamic process. A discussion of shock could cover many pages. For most people, it is simply important to understand that the circulation is not occurring as designed or that blood is not flowing properly through the body in a "shocky" cat.

Several different sub-classifications of shock will help further understand the problem.

Hemorrhagic shock occurs when blood, for some reason, is lost from the system. There then is less blood available to pump through the body. Hypovolemic shock occurs in many diseases that lead to dehydration, which is a lack of water in the system. Cardiogenic shock occurs when the heart, for various reasons, fails to pump the blood through the body properly.

Septic shock or blood poisoning occurs when massive infection enters the blood. Dilation of blood vessels then occurs causing blood to pool in the tissues and not return to the heart for pumping. Anaphylactic shock occurs when an allergic reaction dilates all the blood vessels and blood pools away from the heart thus decreasing circulation. Other forms of shock are also recognized.

All forms of shock will generally lead to signs of profound weakness, cool skin temperature, pale gums and other mucus membranes, a rapid heart rate, rapid, shallow respiration, decreased mental responsiveness and a decrease in core body temperature. Cats with septic shock will have a fever. Left untreated, shock leads to heart failure and death. Diagnosis is based on history, physical examination, blood counts and blood pressure measurements.

The basic aim in treatment of all forms of shock is to restore normal circulation. Generally, IV fluids and electrolytes, bicarbonate injections, injections of cortisone-like drugs, antibiotics for sepsis and oxygen therapy will work towards that end. Warming the patient and the mechanical support of respiration may also be needed. It should be remembered that any initiating factor must be addressed in addition to general treatment and that if organ damage has occurred due to circulatory failure, further complications will be expected.

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