Microbial persistence may be involved in the pathogenesis of idiopathic dilated cardiomyopathy (IDC). Therefore, we evaluated the role of various cardiopathogenic microorganisms in patients with end-stage IDC. In a previous study, we did not find evidence for the persistence of enterovirus RNA in end-stage IDC. In the present study, we looked for other microorganisms that are frequently associated with heart disease, including cytomegalovirus, hepatitis B virus,hepatitis C virus, Borrelia burgdorferi, Chlamydia species, mycoplasmata, and Toxoplasma gondii. Serology, polymerase chain reaction (PCR) analysis specific for detection of microbial genomic sequences, or both investigations were performed on myocardial samples from 37 patients with end-stage IDC. PCR analysis was performed on multiple myocardial samples per patient Thirty-nine patients with end-stage heart disease of known cause were included as controls. On the basis of our serological data and PCR analyses, we did not find any evidence that microbial persistence in the heart is involved in the end-stage disease process of IDC.