OBJECTIVE: Viral myocarditis frequently occurrs in children, but no effective medicines for clinic treatment have been found. This paper aims at studying the effect and mechanism of astragalus injection in the treatment of acute murine myocarditis caused by Coxsackievirus B 3. METHODS: Acute viral myocarditis was induced in 24 Balb/c mice by injection of Coxsackievirus B 3m (CVB 3m ) intraperitoneally. Half of the mice were administered astragalus injection with a dosage of 10 g/kg daily for 7 days (astragalus treated group). The remained received the same amount of normal saline and were used as the control group. On the 8th day after CVB 3m infection, the pathological changes of myocardium were studied. Myocardial perforin expression was detected by reverse transcription polymerase chain reactin (RT PCR) and serum TNF α level was measured by radioimmunoassay. RESULTS: The astragalus treated group showed a significant reduction in myocardial lesions compared with that in the control group. The myocardial perforin expression in the astragalus treated group was much lower than that in the control group [( 1.10 ± 0.07 ) vs ( 1.31 ± 0.12 ); P< 0.01 ]. The serum TNF α level was also significantly lower in the astragalus treated group than that in the control group [( 2.39 ± 0.21 ) vs ( 2.97 ± 0.32 ; P< 0.01 )]. The myocardial perforin expression was significantly positively correlated with the serum TNF α level (r= 0.84 , P< 0.01 ). CONCLUSIONS: Astragalus has protective effects against viral myocarditis by reducing perforin mediated cytotoxicity and inflammatory reaction.