The genetically inbred cardiomyopathic Syrian hamster provides a valuable model of congestive cardiomyopathy: myocytolytic necrosis at 30-50 days of age is followed by cardiac hypertrophy at 150-250 days, and finally by congestive failure and death at 250-350 days. Successful drug treatment has been reported in the prenecrotic stage, but not when started during congestive failure. The present study evaluated survival of the cardiomyopathic hamster treated with the new beta-adrenoceptor blocker nebivolol, which was initiated during congestive failure. Fifty animals (BIO82.62, either sex, age 200 days) were acclimated to an environmentally controlled room for 20 days, receiving food and water ad libitum; seven hamsters died, indicating development of congestive failure. The remaining animals were then randomly assigned to one of three groups: 15 animals received control food; food for the others was supplemented with nebivolol, yielding a daily intake of either 0.1 mg/kg (n = 14) or 1 mg/kg (n = 14). At the lower nebivolol dose, death rate was unaltered in comparison with controls. However, at 1 mg/kg, survival was markedly improved (p = 0.042). Nebivolol treatment, started during congestive failure, thus significantly delays mortality in the cardiomyopathic hamster.