By including immunohistochemical parameters the WHF Task Force for the Definition of Acute and Chronic Myocarditis expanded the light microscopical Dallas criteria of myocarditis. The rapid development of new molecular biological techniques such as polymerase chain reaction (PCR) and in-situ hybridization has improved our understanding of the underlying etiological and pathophysiological mechanisms in inflammatory heart disease. Treatment of dilated cardiomyopathy with inflammation is still controversial, however. The American Myocarditis Treatment Trial could not demonstrate a significant difference in the improvement of ejection fraction between patients with active myocarditis in the cyclosporine/prednisolone treated group when compared to placebo. In the European Study of Epidemiology and Treatment of Inflammatory Heart Disease (ESETCID) patients with acute or chronic myocarditis are treated specifically according to the etiology of the disease. Patients are screened not only for infiltrating cells, but also for the presence of persisting viral genome (enterovirus, cytomegalovirus and adenovirus). By investigating endomyocardial biopsies of 3,055 patients ongoing inflammatory processes in the heart could be found in 17.2%. Only 182 showed a reduced ejection fraction below 45% fulfilling the entrance criteria for the ESETCID trial. These data imply that in symptomatic patients inflammatory heart muscle disease has to be considered regardless of left ventricular function and that endomyocardial biopsy can be an important tool for diagnosis. Virus could be detected in 11.8% (enterovirus 2.2%, cytomegalovirus 5.4%, adenovirus 4.2%). These first epidemiological results of this prospective randomized study demonstrate that viral persistence may contribute to the pathogenesis of inflammatory heart muscle disease, and that in chronic myocarditis viral persistence occurs in a smaller percentage of patients compared to previously published studies which were performed on highly selected patients.