Myocarditis is an inflammation of the heart muscle. It can be caused by viral, bacterial, or parasitic infections, drugs or chemicals, connective tissue or auto-immune disorders, or by radiation.

Myocarditis may occur as a consequence of a variety of diseases, such as rheumatic fever, polio, rubella, and influenza. Its most common cause is a viral infection (e.g. from adenovirus, coxsackie virus, or echovirus).

Myocarditis is a fairly rare disorder, affecting males more often than females (1.5 to 1).