Cultured human myocardial fibroblasts of pediatric origin seem to be a useful species-specific model for studying various heart diseases which involve the myocardial interstitium, for example enterovirus heart disease. Cells were propagated from small samples of human ventricular tissues (0.2 g) obtained from standard surgical procedure for the correction of Fallot-tetralogy. Cultured cells exhibited typical fibroblastoid morphology over a period of 4 months and were uniformly immunoreactive with a monoclonal antibody directed against prolyl-4-hydroxylase, a marker enzyme of fibroblasts. Infection of cell cultures with coxsackievirus B3, a cardiotropic enterovirus, resulted in a typical carrier-state type of virus persistence. Average virus titers of 2.3 x 10(5) plaque-forming units/ml (SD = 9.9 x 10(4)) were maintained over a period of up to 10 weeks by productive infection of about 8-10% of the cell population. Coxsackievirus B3 carrier cultures of human myocardial fibroblasts were used to evaluate in vitro the long-term antiviral effects of recombinant interferon alpha-2a and natural human interferon-alpha. Recombinant interferon-alpha reduced virus yields by 90% with a concentration of 423 IU/ml, whereas with natural interferon-alpha a 90% reduction of virus yields was achieved with concentrations as low as 21 IU/ml. Antiviral effects of both recombinant and natural interferon-alpha were highly specific and not related to inhibition of cell-proliferation (< 50% with interferon-alpha concentrations as high as 6250 IU/ml). Since effective concentrations of interferon-alpha can be easily attained in vivo with subcutaneous application, interferon-alpha (in particular: natural interferon-alpha) may become useful in the treatment of patients with enterovirus myocarditis and enterovirus induced dilated cardiomyopathy.