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 
, 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 
, 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 
. Some people have no symptoms.
Causes of Myocarditis
Myocarditis may result from infectious or noninfectious causes. Many cases are unable to be identified (idiopathic).
In the United States and most other developed nations, infectious myocarditis is most often caused by a viral infection. The most common viral causes in the United States are parvovirus B19 and human herpes virus 6. The SARS-CoV-2 virus COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more sometimes causes myocarditis. In lower resource areas, infectious myocarditis is most often caused by rheumatic fever Rheumatic Fever Rheumatic fever is inflammation of the joints, heart, skin, and nervous system, resulting from a complication of untreated streptococcal infection of the throat. This condition is a reaction... read more 
, Chagas disease Chagas Disease Chagas disease is an infection caused by the protozoa Trypanosoma cruzi, which is transmitted by the bite of a kissing bug (also called an assassin or Triatominae bug). The protozoa ... read more 
, or AIDS Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more 
.
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
People may have only a few symptoms or have severe and rapidly progressing 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 and severe heart rhythm abnormalities 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 . Symptoms depend on the cause of the myocarditis as well as the extent and severity of inflammation.
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.
Myocarditis can be acute, subacute or chronic. In some cases, myocarditis can lead to dilated cardiomyopathy Dilated Cardiomyopathy Dilated cardiomyopathy is a group of heart muscle disorders in which the ventricles (the two lower chambers of the heart) enlarge (dilate) but are not able to pump enough blood for the body’s... read more 
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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.
Cardiac catheterization Cardiac Catheterization and Coronary Angiography Cardiac catheterization and coronary angiography are minimally invasive methods of studying the heart and the blood vessels that supply the heart (coronary arteries) without doing surgery. These... read more 
may be useful for ruling out a decrease in blood flow to the heart because myocarditis can mimic a heart attack Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more 
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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
Treatment of heart failure includes diuretics and nitrates for symptomatic relief. In some cases of heart failure, a surgery such as placement of a left ventricular assist device Other measures 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 (LVAD), or heart transplantation Heart Transplantation Heart transplantation is the removal of a healthy heart from a recently deceased person and then its transfer into the body of a person who has a severe heart disorder that can no longer be... read more may be necessary. Long-term drug treatment of heart failure Drugs for heart failure 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 is needed.
Abnormal heart rhythms are treated with antiarrhythmic therapy Drugs to Treat Abnormal Heart Rhythms There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more . Sometimes a pacemaker Artificial Pacemakers There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more 
is needed if abnormal heart rhythms persist.
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.
Giant cell myocarditis is treated with corticosteroids and immunosuppressive therapy Medications Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
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Myocarditis caused by sarcoidosis is treated with corticosteroids.
