Definition:

Myocarditis is clinically defined as cardiac disease associated with inflammation of the myocardium and necrosis and/or degeneration of adjacent myocytes in the absence of an ischemic event. Most often, myocarditis results from common viral infections; less commonly, specific forms of myocarditis may result from other pathogens, toxic or hypersensitivity drug reactions, giant-cell myocarditis, or sarcoidosis. More than 20 common viruses, including coxsackieviruses, adenoviruses, influenza viruses, cytomegaloviruses, and human immunodeficiency virus, have been associated with myocarditis in humans. However, coxsackieviruses are considered the dominant cause of myocarditis, particularly in neonates and young children. After the acute phase caused by direct cytopathic effects of the virus, a small proportion of patients subsequently develop autoimmune- mediated, chronic myocarditis, accompanied by circulating autoantibodies to cardiac myosin and other heart antigens, which can sometimes lead to heart failure and death associated with dilated cardiomyopathy (DCM). Genetic linkage between susceptibility to myocarditis/DCM and the major histocompatibility complex (MHC) genes has been reported in both humans and experimentally induced mouse models.