The clinical picture of myocarditis/myopericarditis is of importance in differential diagnosis, especially in younger patients with suspected myocardial infarction. Myocarditis/myopericarditis commonly presents with chest pain, and the diagnosis is usually established on clinical grounds. However, endomyocardial biopsy is necessary to confirm the diagnosis. We evaluated the characteristics of acute myocarditis over the years 1980-1998 in 54 patients of the Department of Medicine of the University Hospital, Zurich. Two to 6 patients per year were hospitalised with this diagnosis. In most cases the diagnosis was established by a combination of criteria, such as a preceding infection of the upper respiratory tract, thoracic pain, ST segment elevations in different precordial leads followed by T wave inversions, arrhythmias, elevation of cardiac enzymes, reversible hypokinesia by echocardiography and normal coronary arteries. At least 3 of 5 criteria were requested. In a first step we analysed retrospectively all patients with acute myocarditis/myopericarditis in the years 1980-1993. Among 30 cases of acute myocarditis/myopericarditis the following causes could be identified: one influenza B, one Toxoplasma gondii infection, 2 Epstein-Barr infections and one bacterial myocarditis with gram-negative rods. The aetiology of the other 25 cases remained unknown. The majority of myocarditis/myopericarditis healed without complications. One patient with Epstein-Barr myocarditis and one with Toxoplasma gondii infection died. Two patients developed dilated cardiomyopathy. In a second phase we analysed prospectively all cases with acute myocarditis/myopericarditis over the period 1994-1998: 24 patients with acute myocarditis/myopericarditis were hospitalised. At that time coronary angiography and endomyocardial biopsies were performed more frequently. We found 2 patients with giant cell myocarditis and 2 with Toxoplasma gondii infection and HIV, all of whom died. In addition, there were 2 patients with eosinophilic myocarditis, one with Lyme carditis, one with Epstein-Barr myocarditis, one with myopericarditis after Campylobacter enteritis and one histologically proven myocarditis after pneumonia with Haemophilus influenzae. The aetiology of the remaining 13 cases with myocarditis/myopericarditis could not be established. Three patients with probable viral myocarditis developed cardiogenic shock requiring intraaortic balloon pump, and fully recovered. The patient with Lyme carditis manifested with total atrioventricular block and was treated with a temporary pacemaker. One patient with lymphocytic myocarditis required heart transplantation because of terminal heart failure and one female patient with histologically proven diffuse lympho-monocytic myocarditis died of cardiogenic shock. All the other cases healed without complications. Serologies are of little diagnostic value and should be restricted to serologies with therapeutic implications. We believe that the apparent increase in myocarditis/myopericarditis in recent years is a result of better diagnostic tools, such as more specific cardiac enzyme tests, coronary angiography and endomyocardial biopsies. In most cases the therapy remains symptomatic. In elected, severe cases steroids and other immunosuppressive drugs are sometimes used.