We have previously demonstrated that administration of nitric oxide (NO) synthase inhibitor, N G -nitro-l-arginine methyl ester (l-NAME), aggravated murine coxsackievirus B3 myocarditis. In the present study, we evaluated the effects of l-arginine, a precursor of NO, upon acute and chronic myocarditis. Dietary l-arginine and l-arginine plus l-NAME (l-arginine+l-NAME group) were administered to coxsackievirus B3 (CB3)-infected C 3 H/He mice for 2 weeks (experiment I), and to CB3-infected mice from the second week until the fourth week after virus inoculation (experiment II). Infected control was prepared in each experiment. In experiment I, survival was higher in the l-arginine group compared with the other two groups, and cardiac damage was less. In addition, plasma concentrations of l-arginine and NO were elevated in the l-arginine group. In experiment II, cardiomyopathic lesion in the l-arginine group was less prominent associated with lower plasma catecholamine and lower myocardial collagen concentrations compared with the other two groups. Thus, l-arginine treatment may be effective not only in preventing the development of acute CB3 myocarditis but in ameliorating cardiac dysfunction in chronic myocarditis.