Myocarditis refers to an inflammation of the myocardium, the middle and thickest layer of the heart wall, that aids in overall proper functioning of the heart. The disease can lead to cell degeneration or stiffening and hardening of the heart.

Heart inflammation in cats, also known as myocarditis, is an extremely rare condition. Although it can affect any cat at any time, cats younger than eight years old are the most commonly affected. The disease can take days or weeks to develop often with no signs of any trouble until after the cat is found dead. Sudden death is common and is due to a disturbance in the heart’s natural rhythm, which may be attributed to a previously undetected infectious disease and the ability of the cat’s immune system to respond to it. It can also be caused by chemical or abnormal physical conditions.

Symptoms are usually few since the disease is so acute. However, if caught in time, these are the signs that your cat may exhibit. If you observe these signs, take your cat to your veterinarian immediately as it is an extreme emergency situation. 

There are two main types of myocarditis, primary and secondary.

Primary Carditis is mainly due to systemic infection and most commonly leads to hypertrophic cardiomyopathy in which the left side of the heart has become thickened and can no longer fully relax, refill with blood, and contract. It manifests as Chagas’ myocarditis in the southern United States or Lyme (tick borne) myocarditis in the northeastern United States.

Secondary Carditis develops out of a defined disorder such as hypertension, hyperthyroidism, taurine deficiency, growth hormone excess, and sometimes anemia and diabetes.

Viral infection is the most common cause of myocarditis, but there are a few others.

After a physical examination to check for murmurs or unusual sounds and to find your cat’s blood pressure, your veterinarian will want to conduct a series of tests to verify the extent of the disease and to determine if there are any underlying conditions. Diagnosis is primarily based on suspicion and elimination of the possibility of other diseases. 

Your cat will need to be hospitalized and treated immediately if there are any signs of myocarditis. Treatment will be targeted at improving the heart’s contraction, relieving congestion, and reducing constriction. Your cat will be anesthetized during treatment. There is a risk of sudden death while your cat is being anesthetized because of the heart’s fragile condition. Be sure to talk to your veterinarian about how he or she will manage the procedure.

There are many medications that your veterinarian may opt to use in stabilizing your cat’s heart and providing relief depending on what your cat is experiencing. 

Beta-blockers can be used to slow the heart rate down if there is tachycardia. It will also decrease stress on the heart and reduce its need for oxygen.

One of several types of muscle relaxers may be chosen if the heart is restrictive due to the beginnings of cardiomyopathy (stiffness of the heart wall).

If the heart is failing to contract properly because of congestive heart failure (weakness), medication will be prescribed to help the heart to contract properly.

ACE inhibitors and diuretics will be administered to relieve hypertension and congestion if heart failure has occurred and if pericarditis (inflammation of the pericardial sac surrounding the heart causing excessive fluid buildup and pressure) is present.

Blood clots can be common if the heart is experiencing cardiomyopathy. Certain blood thinners to decrease the possibility of blood clots forming may be utilized.

Any additional necessary medications such as antibiotics and anti-inflammatories will be prescribed to treat any underlying disease. Since myocarditis is often attributed to such diseases, your veterinarian will want to be aggressive in addressing these conditions. 

A pacemaker may be implanted if there is a congenital abnormality of the atrial valve that is keeping the heart from maintaining a proper rhythm. 

How your cat responds to treatment largely depends on your cat’s immune response to the inflammation as it will indicate any structural or functional abnormalities. If the myocarditis has become severe and has led to congestive heart failure, the prognosis may be poor. Likewise, if arrhythmia or cardiomyopathy is determined then the prognosis will be guarded. However, most cats will live many years as long as the disease is properly managed and stabilized.

Most cats with congestive heart failure require medications for the remainder of their lives. Regular blood tests, x-rays, and echocardiograms will be needed to monitor your cat’s condition as well. 

At home, be sure to keep your cat away from stress at all times if possible after treatment to help with recovery, and limit any activity until your veterinarian tells you it is okay for your cat.

You should also be continuously watchful for any labored breathing or irregular breathing rates. If you observe your cat having these symptoms, take it to the veterinarian right away.

Changes in diet may be necessary, especially concerning sodium intake. If your cat was found to be deficient in taurine, it is mainly because your cat was receiving non-commercial or homemade food. You may be instructed to feed your cat a specific commercial cat food since they are often rich in taurine, a very important ingredient in heart health. Your veterinarian can make a good recommendation for you. 

There is no effective cure for myocarditis, so your cat will be treated and supported for any associated diseases that your veterinarian has found to be the root cause. With regular testing, medication, and moderation in activity, your cat may live for many years.