What is myocarditis?

Myocarditis refers to inflammation of the heart muscle. It is most often due to a virus. Other causes include drug abuse and conditions such as systemic lupus erythematosus (SLE).

Myocarditis due to a virus is relatively common, but most cases are very mild and are never seen by a doctor. However, some cases are severe and can lead to considerable damage to the heart pump, resulting in severe heart failure and even dangerous arrhythmia.


People may feel feverish and have generalised aches and pains as with any other viral illness. When the heart is severely affected a person may feel tired and breathless. Chest pain and palpitations are relatively common under these circumstances. Apart from a rapid heart rate, the doctor may not find any other abnormalities if there is only mild myocarditis. However, if it is severe there may be evidence of heart failure and/or arrhythmia.

How is myocarditis diagnosed?

The presence of a flu-like illness and fever may raise the suspicion of myocarditis in someone with symptoms. Simple blood tests may, however, show signs of inflammation and heart damage. The ECG may show changes which can come and go, are non-specific and can occur in other heart diseases. An ECHO can show an enlarged heart, which pumps poorly. The diagnosis can be confirmed by a biopsy (a small sample) taken from the heart. An MRI scan can be useful for diagnosing inflamed heart muscle.

In very mild cases, both the ECG and the ECHO may be normal, so when symptoms of a flu-like illness are present, a person should be cautious and not take part in any exercise or sports until they have recovered fully.


Patients should rest until symptoms settle. Patients with heart failure and arrhythmia must stay in hospital for treatment of these (see the section on dilated cardiomyopathy). Steroids may be used in specific forms of myocarditis. Patients should not take part in any exercise or sports until all symptoms have settled and the ECG and ECHO are back to normal. Over three quarters of people will improve within two weeks without any complications. Around 1 in 10 patients may then develop dilated cardiomyopathy and require lifelong treatment for heart failure.