Patient Basics: Myocarditis

Originally published by Harvard Health.

What Is It?

Myocarditis is an inflammation of the heart muscle that decreases the ability of the heart to pump blood normally. It can be caused by:

  • An infection —Many infections have been associated with myocarditis. Some of the more likely germs include:
    • Viral infections — A common cause of myocarditis. Many different viruses can cause myocarditis. Examples include adenovirus, coxsackievirus, Epstein-Barr virus, HIV, varicella (chickenpox) and human herpes virus 6.  Often the person has no preceding symptoms of a cold, cough, nasal congestion or rash and only becomes aware of the infection when heart failure occurs.
    • Bacteria — Rarely, myocarditis is a complication of endocarditis, an infection of the heart valves and the lining inside the heart’s chambers caused by bacteria. In some people with diphtheria, a toxin (poison) produced by C. diphtheriae bacteria causes a form of myocarditis that leads to a flabby, stretched-out heart muscle. Because the flabby, enlarged heart cannot pump blood efficiently, severe heart failure may develop within the first week of illness.
    • Chagas’ disease — This infection, caused by the protozoan Trypanosoma cruzi, is transmitted by an insect bite. In the United States, myocarditis caused by Chagas’ disease is most common among travelers to or immigrants from Central and South America. In up to one-third of people with Chagas’ disease, a form of chronic (long-term) myocarditis develops many years after the first infection. This chronic myocarditis leads to significant destruction of heart muscle with progressive heart failure.
    • Lyme myocarditis — Lyme disease, an infection caused by the tick-borne bacterium Borrelia burgdorferi, can cause myocarditis or other heart problems.
  • Toxic substances and certain medications — Myocarditis also can be caused by:
    • Overuse of alcohol
    • Radiation,
    • Chemicals (hydrocarbons and arsenic)
    • Certain medicines, such as doxorubicin (Adriamycin)drugs,
  • Inflammatory diseases — This includes systemic lupus erythematosus (SLE or lupus) and other autoimmune diseases and sarcoidosis.


Another type of myocarditis is peri-partum cardiomyopathy. For unexplained reasons, some women in the very last phase of pregnancy or soon after delivery of the baby develop poor heart muscle function. This condition is unusual.


The symptoms of myocarditis depend on the cause and severity. For example, many people with uncomplicated myocarditis caused by coxsackievirus don’t have any symptoms. The only sign of heart inflammation may be a temporary abnormal result on an electrocardiogram (EKG), a test that measures the heart’s electrical activity. Or an echocardiogram may show some abnormalities, such as decreased strength of heart contractions. Other people have fever, chest pain, cardiac arrhythmias (abnormally fast, slow or irregular heartbeats), sudden loss of consciousness (syncope) or signs of heart failure (shortness of breath, leg swelling).


Your doctor will suspect myocarditis based on your medical history and symptoms. To confirm the diagnosis, your doctor will examine you, paying special attention to your heart. This will be followed by an EKG, a chest X-ray, an echocardiogram and blood tests.

In some patients, your doctor may order tests to determine if a virus or other infectious agent is the cause. These tests in include blood tests and attempts at isolating certain types of viruses from stool, throat washings or other body fluids.

Expected Duration

How long myocarditis lasts depends on the cause and on the patient’s general health. For example, in many typically healthy adults with uncomplicated coxsackievirus myocarditis, symptoms can start to improve over a couple weeks. In other cases, the heart takes a few months to recover. Sometimes, the damage to the heart muscle is permanent and heart failure persists after the inflammation has resolved.


Myocarditis caused by infections can theoretically be avoided by practicing good hygiene, especially washing your hands often. Diphtheria myocarditis can be prevented by undergoing diphtheria immunization, and HIV can be prevented by following safe sex practices and avoiding intravenous drug use. Myocarditis caused by insect-borne Chagas’ disease can be prevented by using effective insecticides in Latin American countries where the illness is common.


Treatment of myocarditis depends on the cause and severity. For example, people with only mild viral myocarditis may be allowed to rest at home. They will be advised not to smoke or to drink alcohol. They will need to limit strenuous activities.

People with myocarditis that causes heart failure or cardiac arrhythmias will be treated in a hospital. There they will receive one or more of the following:

  • Oxygen
  • Medication or a pacemaker to treat or prevent cardiac arrhythmias
  • Medication, including diuretics and vasodilators, to treat heart failure
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve pain
  • Anticoagulants to prevent blood clots
  • Antibiotics to treat bacterial myocarditis or Lyme disease
  • Diphtheria antitoxin and antibiotics to treat diphtheria myocarditis
  • Glucocorticoid medication to treat autoimmune diseases and sarcoidosis.

When To Call a Professional

Call your doctor immediately if you have chest pain, even if you think that you are too young to be having heart problems. People of any age can get the chest pain of myocarditis, with or without other symptoms (fever, shortness of breath, abnormal heartbeat, leg swelling).


In many people with uncomplicated viral myocarditis, the heart muscle changes improve without specific therapy and myocarditis-related EKG and echocardiogram abnormalities eventually disappear. However, more severe forms of myocarditis can cause permanent damage to the heart muscle.

Additional Info

National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: 301-592-8573
TTY: 240-629-3255