OBJECTIVE: To study the curative effect of two Chinese traditional medicines, astragalus membranaceus and folium isatidis, on murine viral myocarditis (VMC). METHODS: Balb/C mice were injected intraperiloneally with a diluted solution of coxsackievirus B3 (CVB3), and then randomly divided into three groups; infected control group, astragalus membranaceus treated group and folium isatidis treated group. The mice were sacrificed on days 3, 5, 7, 10, 14 and 21 after injection. The myocardial pathological score was estimated and viruses from myocardium were separated. In addition, the myocardial ultrastructure was detected under electon microscope on day 7 of post-injection. RESULTS: Compared with the myocardial pathological score of the infected control group, thxxse of both the astragalus membranaceus treated group (from day 5 to day 21) and folium isatidis treated group (on day 5 and day 7 post-injection) were significantly decreased ( P <0.05). There was no difference in the myocardial score after 10 days of infection between the folium isatidis group and the infected control group. The ultrathin section of myocardium in the infected control group revealed mitochondria! swelling, mitochondrial crista rupture and sarcoplasmic reliculum dilatation under electron-microscope. The pathological changes were relieved after treatment in both the astrgalus membranaceus and folium isatidis groups. Moreover, there were a lot of lysosomes in myocardium of the folium isatidis treated group. The results of viral isolation were positive on day 3 of post-infection in the three groups, with the same positive rate of 66. 7% . The same positive rate of viral isolation (100% ) was also found from day 5 to day 10 of post-infection in the three groups. On day 14 of post-infection, the positive viral isolation was noted only in the infected control group (33.3%) but failed in all three groups on day 21 of post-infection. CONCLUSIONS: Astragalus membranaceus may have a protective effect on myocardial cells. Folium isatidis could relieve myocardial lesions in the early stage of CVB3-induced myocarditis.