The World Health Organization/International Society and Federation of Cardiology (WHO/ISFC) task force on the definition and classification of cardiomyopathies recently updated and reclassified heart muscle diseases.1 Myocarditis was defined as “an inflammatory disease of the myocardium . . . diagnosed by established histological, immunological, and immunohistochemical criteria.” Three distinct forms of inflammatory cardiomyopathy (that is, myocarditis associated with cardiac dysfunction) are recognised: idiopathic, autoimmune, and infectious. Various infectious factors may cause myocarditis, but viral agents, especially coxsackie group B viruses, are most commonly associated with this disease.2

Myocarditis has been recognised for almost two centuries, since Corvisart first described this disease in clinical terms in 1812,3 but in the last three decades there has been renewed interest in the inflammatory process in the myocardium. The reasons for this are multiple: the introduction of endomyocardial biopsy for in vivo diagnosis (the disease was often overdiagnosed in the past on purely clinical grounds)4; related efforts to produce standardised criteria for histological diagnosis (the Dallas criteria; fig 1)5; better understanding of cardiotropic viruses, studied in animal models of myocarditis,6 leading to new insights into the immunological mechanisms of the disease (fig2)7 and potential treatments in humans8; and lastly—and perhaps most interestingly—the finding of a possible causal relation between viral myocarditis and dilated cardiomyopathy,9 a major cause of congestive heart failure in western countries.

Despite numerous published reports on this disease, the natural history of acute myocarditis is still poorly understood, despite the development of immunological …