Enteroviruses are known to have association with human myocarditis and dilated cardiomyopathy (DCM). We screened biopsy specimens from patients with active myocarditis or DCM, and myocardial tissues from autopsy cases without cardiac diseases using polymerase chain reaction (PCR) gene amplification. Positive enteroviral signals were demonstrated from 4 of 5 patients with active myocarditis (80%), 7 of 42 patients with DCM(17%) and 3 of 27 autopsies (11%). Out of 7 PCR positive patients with DCM, 3 cases showed hypertrophy and disarray of cardiocytes, fibrosis in the interstitium, and a few inflammatory infiltrates. The remaining 4 cases with DCM and 3 PCR positive autopsy cases did riot exhibit histological findings compatible with those in myocarditis. Our results support the observations that enteroviruses are common aetiologic agents of myocarditis, and some cases of DCM. Our results also suggest the possibility that in some cases enteroviruses may persist in the myocardium without causing apparent pathological changes.