Infection by enteroviruses, especially by Coxsackie B viruses, has been incriminated in pathogenesis of dilated cardiomyopathy. We developed polymerase chain reaction tests for the detection of enteroviral and Coxsackie B3 genomes, respectively, in myocardial biopsies obtained from a homogeneous group of 19 patients with idiopathic dilated cardiomyopathy. To determine unambiguously the incidence of enteroviruses and Coxsackie B3 viruses in these patients, we used two primer pairs, one common to all enteroviruses and the other specific for Coxsackie B3 viruses. In six patients of the dilated cardiomyopathy group, enteroviral ribonucleic acid (RNA) could be detected; only one was subspecified as Coxsackie B3 RNA. In contrast, no enteroviral RNA could be detected in a contrast group of 21 patients with other cardiac disorders. These results suggest that enteroviruses other than Coxsackie B3 are causally linked to the pathogenesis of dilated cardiomyopathy.