What Is It?

Myocarditis is an inflammation of the heart muscle. It can be caused by:

  • Viral infection — This common form of myocarditis often occurs after a viral infection of the nose and throat and often goes away on it own after it runs its course. Although many different viruses have the potential to produce myocarditis, coxsackievirus B is the most common culprit in the United States. Other viruses capable of causing myocarditis include echovirus, influenza (flu), Epstein-Barr, rubella, varicella (chickenpox), mumps and hepatitis.

  • HIV infection — About 10 percent of people with HIV develop myocarditis, either because HIV directly invades the heart muscle or because the patient’s weakened immune system makes the heart muscle more susceptible to attack by other infectious agents, especially toxoplasmosis.

  • Bacterial infection — Rarely, myocarditis occurs as a complication of endocarditis, an infection of the heart valves and the lining inside the heart’s chambers caused by bacteria. Some common bacteria responsible for myocarditis include Staphylococcus aureus, enterococci and Corynebacterium diphtheriae (the cause of diphtheria). In about 25 percent of 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 congestive 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 or immigrants from Central and South America. In up to one-third of people with Chagas’ disease, a form of chronic myocarditis develops many years after the initial infection. This chronic myocarditis leads to significant destruction of heart muscle with progressive heart failure.

  • Lyme myocarditisLyme disease, an infection caused by the tick-borne bacterium Borrelia burgdorferi, causes myocarditis or other heart problems in about 10 percent of patients.

  • Giant-cell myocarditis — This rare form of myocarditis takes its name from large, abnormal giant cells that are found when a piece of the affected heart muscle is examined under a microscope. Giant-cell myocarditis is most common among patients suffering from thymoma (a growth of the thymus gland, which is a collection of immune system tissues below the top of the breastbone), systemic lupus erythematosus (SLE or lupus), or thyrotoxicosis (a very overactive thyroid), but its true cause remains a mystery. The illness usually strikes young adults, and it can quickly lead to death from heart failure and/or cardiac arrhythmia (abnormal heartbeat).

  • Other agents — Myocarditis also can be caused by alcohol, radiation, chemicals (hydrocarbons and arsenic), and drugs, including doxorubicin (Adriamycin, Rubex), cyclophosphamide (Cytoxan, Neosar), emetine, chloroquine (Aralen) and sulfonamides (Gantanol, Gantrisin, Thiosulfil Forte, Urobak).


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, and their only sign of heart inflammation is a temporary abnormal result on an electrocardiogram (EKG), a test that measures the heart’s electrical activity. 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, and blood tests. In patients with myocarditis that has triggered signs of more severe heart damage, an echocardiogram and/or other specialized heart tests may be necessary to check for abnormalities in the size of the heart and how it functions.

In some patients, blood tests may be done to check whether myocarditis is related to Epstein-Barr virus, hepatitis viruses, HIV or another virus. Some medical centers also have the capability to isolate certain types of viruses from the patient’s 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 B myocarditis, symptoms go away within a few days.

In cases in which myocarditis causes significant damage to the heart muscle, the patient may suffer from heart failure or potentially lethal heart arrhythmias. These problems can develop within a matter of days (diphtheria-related myocarditis), or they can occur after many years of chronic myocarditis (Chagas’ disease).


Many cases of myocarditis caused by infections can 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 the use of effective insecticides in Latin American countries where the illness is common. A new vaccine recently has been approved to prevent Lyme disease.


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

Patients whose myocarditis produces 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, digoxin (Lanoxin) and vasodilators, to treat heart failure
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve pain
  • Anticoagulants to prevent blood clots
  • Antibiotics, usually given intravenously, to treat bacterial myocarditis or Lyme disease
  • Diphtheria antitoxin and antibiotics to treat diphtheria myocarditis
  • Glucocorticoid medication to treat giant-cell myocarditis

When To Call A Professional

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


In most patients with uncomplicated viral myocarditis, the illness goes away on its own, and any myocarditis-related EKG abnormalities eventually disappear. However, more severe forms of myocarditis can cause permanent, even deadly, damage to the heart muscle.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

  A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.