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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

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.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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