The present authors recently suggested, on the basis of studies using polymerase chain reaction (PCR), that hepatitis C virus (HCV) infection is involved in the etiology or pathogenesis of cardiomyopathic disorders. They have also reported that the serum concentration of cardiac troponin T is an indicator of ongoing myocyte degeneration in patients with dilated cardiomyopathy (DCM) and hypothesized that its serial measurement may be a marker of therapeutic efficacy. This is the first case report of DCM and striated myopathy, associated with HCV infection, treated with interferon therapy guided by monitoring of serial serum concentrations of cardiac troponin T. Positive-plus strands of HCV RNA were found in the patient's myocardium, as well as plus and minus strands in the quadriceps muscle specimens. Serum levels of creatine kinase (CK), CK-MB and cardiac troponin T fell as serum HCV titers decreased during treatment with interferon, whereas conventional treatment of heart failure had no effect. Monitoring of serial serum concentrations of cardiac troponin T may allow the earlier diagnosis and treatment of patients with HCV-associated cardiomyopathy and improve their clinical course.