Despite all our efforts, the clinical diagnosis viral myocarditis is usually only a tentative one. This diagnosis can be established with a high degree of probability only on the basis of a combination of virological, histological and immunohistological findings in myocardial biopsies. The use of highly specific monoclonal antibodies against lymphocyte subpopulations and histocompatibility antigens makes possible a differentiated consideration of the diagnosis, severity and course of the disease. Although the etiopathogenesis, the natural course and the destructive mechanisms of the viral heart disease have not yet been finally clarified, numerous clinical and experimental findings indicate that underlying the viral myocarditis or the resulting dilatative cardiomyopathy is a viral infection-induced loss of self-tolerance with subsequent autoaggression against myocardial structures.