Merck Manual

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Brian D. Hoit

, MD, Case Western Reserve University School of Medicine

Reviewed/Revised Jul 2022 | Modified Sep 2022
Topic Resources

Myocarditis is inflammation of the muscle tissue of the heart (myocardium) that causes tissue death.

  • Myocarditis may be caused by many disorders, including infection, toxins and drugs that affect the heart, and systemic disorders such as sarcoidosis, but often the cause is unknown.

  • Symptoms can vary and can include fatigue, shortness of breath, swelling (edema), awareness of heart beats (palpitations), and sudden death.

  • Diagnosis is based on electrocardiography (ECG), measurement of cardiac biomarkers, imaging of the heart, and biopsy of the heart muscle.

  • Treatment depends on the cause and includes drugs to treat heart failure and arrhythmias and rarely surgery.

Inflammation can be spread throughout the heart muscle or confined to one or a few areas. If inflammation extends into the pericardium (the flexible two-layered sac that envelops the heart) , this causes myopericarditis. The extent of myocardial involvement and extension into the pericardium can determine the type of symptoms. Inflammation that is spread throughout the heart may cause heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more Heart Failure (HF) , abnormal heart rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more Overview of Abnormal Heart Rhythms , and sometimes sudden cardiac death. Less widespread inflammation is less likely to cause heart failure but can still cause abnormal heart rhythms and sudden cardiac death. Involvement of the pericardium leads to chest pain and other symptoms typical of pericarditis Overview of Pericardial Disease Pericardial disease affects the pericardium, which is the flexible two-layered sac that envelops the heart. The pericardium helps keep the heart in position, helps prevent the heart from overfilling... read more Overview of Pericardial Disease . Some people have no symptoms.

Causes of Myocarditis

Myocarditis may result from infectious or noninfectious causes. Many cases are unable to be identified (idiopathic).

Noninfectious causes include substances that are toxic to the heart (such as alcohol and cocaine), certain drugs, and some autoimmune and inflammatory disorders. Myocarditis may also occur after mRNA-based COVID-19 vaccination COVID-19 Vaccine Coronavirus disease 2019 (COVID-19) vaccines provide protection against COVID-19. COVID-19 is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines... read more and is rare. It occurs mostly in adolescent and young adult males, usually within a week of vaccination. Myocarditis caused by drugs is termed hypersensitivity myocarditis.


Giant cell myocarditis

Giant cell myocarditis is a rare, severe form of myocarditis that has a rapid onset. The cause is unclear but may be autoimmune. A biopsy is done for diagnosis. In people with giant cell myocarditis, the heart is suddenly unable to pump enough blood to support the body's functions (called cardiogenic shock). People also frequently have abnormal heart rhythms that are hard to correct. Giant cell myocarditis has a poor prognosis but immunosuppressive therapy can help improve survival.

Symptoms of Myocarditis

Heart failure symptoms may include fatigue, shortness of breath and swelling (edema).

Some people may have an awareness of heartbeats (palpitations) or fainting. In some people, the first symptom is a sudden, severe abnormal heart rhythm.

When inflammation of the pericardium occurs along with myocarditis, people may have chest pain. Dull or sharp pain may spread to the neck, back, or shoulders. Pain ranges from mild to severe. Chest pain due to pericarditis is usually made worse by movement of the chest such as coughing, breathing, or swallowing food. Pain may be relieved by sitting up and leaning forward.

People with infectious myocarditis may have symptoms of the infection, such as fever and muscle aches before myocarditis develops. Drug-related or hypersensitivity myocarditis may be accompanied by a rash. Some people may have enlarged lymph nodes.

Diagnosis of Myocarditis

  • Electrocardiography (ECG) and measuring cardiac markers

  • Cardiac imaging

  • Sometimes, endomyocardial biopsy

  • Tests to identify cause

Doctors suspect myocarditis when otherwise healthy people with no risk factors for heart disease have with symptoms of heart failure or abnormal heart rhythms.

ECG is done to look for evidence of a heart problem.

Doctors measure levels of cardiac markers (substances that are present when the heart is damaged) in the blood.

Echocardiography can show abnormalities in people with myocarditis.

Cardiac magnetic resonance imaging may show a characteristic pattern of abnormalities in people with myocarditis.

Endomyocardial biopsy in which a doctor takes a sample of tissue from the inner wall of the heart to examine under a microscope, can be done to confirm myocarditis. However, because a diagnosis depends on the doctor obtaining a tissue sample from an area that shows the disease, endomyocardial biopsy may not be the best test for diagnosing myocarditis. Therefore if endomyocardial biopsy shows evidence of myocarditis, the disorder is confirmed, but just because a tissue sample does not show signs of myocarditis does not mean this diagnosis can be eliminated. In addition, because endomyocardial biopsy carries risks of severe complications, including a tear in the wall of the heart and death, it is not routinely done unless doctors suspect giant cell myocarditis (because prompt treatment of giant cell myocarditis may be life saving) or if myocarditis causes severe heart failure or heart rhythm abnormalities.

Diagnosis of cause

After myocarditis is diagnosed, tests to determine the cause are done. In a young, previously healthy adult who has a viral infection and myocarditis, an extensive evaluation is usually not necessary.

A complete blood count is helpful to look for certain types of white blood cells (eosinophils), which are present in large numbers in people with hypersensitivity myocarditis usually due to a drug allergy.

In other cases, a biopsy of heart tissue may be needed to establish a diagnosis.

Other tests, including tests for autoimmune disorders, human immunodeficiency virus infection, histoplasmosis, and other infections, may be needed.

Treatment of Myocarditis

  • Treatment of heart failure and abnormal heart rhythms

  • Treatment of underlying disorder

Antibiotics or drugs to treat other types of infections may sometimes be given if myocarditis is caused by an infection.

When a drug or toxin causes myocarditis, the causative substance is stopped and corticosteroids are given.

Myocarditis caused by sarcoidosis is treated with corticosteroids.

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