OBJECTIVE To observe the protective effect of compound acanthopanax senticosus injection (CASI) on myocardial ischemia-reperfusion arrhythmia in rats. METHODS The myocardial ischemia-reperfusion model was induced by 30 min coronary occulusion and 60 min reperfusion in openchest anesthetized rats. The changes of arrhythmia with electrocardiogram lead II, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), the contents of malondialdehyde (MDA) and Ca2+ in myocardium were determined. RESULTS In rats treated by CASI (in a dosage of 25, 50 and 100 mg x kg(-1) femoral vein infusion at 30 min after coronary occulusion), the incidence of myocardial ischemia-reperfusion ventricular arrhythmias, for instance the ventricular tachycardia (VT) and ventricular fibrillation (Vf), was effectively prevented, the appearing time of arrhythmia was delayed and the duration of arrhythmia was shortened, while the elevated ST segment lowered as well. At the same time, the contents of myocardial Ca2+ and MDA were decreased significantly as well as the activities of myocardial SOD and GSH-Px increased markedly. CONCLUSIONS CASI is of protective effect on myocardial ischemia-reperfusion arrhythmia, which may be related to scavenging the oxygen free radicals and Ca2+ overload formed during reperfusion.