A murine model for observing the effect of Astragalus membranaceus (AM) on electrophysiological action of the right ventricular myocardium was developed in 4-week-old male BALB/c mice infected with coxsackie B-3 virus (CB3V). The conventional microelectrode technique and a real-time data processor system were used. The survival rate in AM-treated mice was much higher and the percentage of abnormal action potential was much lower than those in infected control mice (P < 0.05, P < 0.01, respectively). Some abnormal electrophysiological parameters, such as APA, OS and Vmax, in infected myocardium were found to be improved by AM treatment. The results suggest that AM may be valuable in the prevention and treatment of acute viral myocarditis involving coxsackie B viruses.