The effects of an ethanol extract of the plant Sophora flavescens Ait. on cardiac arrhythmias induced by coronary artery ligation in rats, and by aconitine infusion in mice, were studied. Pretreatment with intravenous injection of the extract, 120 mg/kg, significantly reduced the incidence and delayed the onset of ventricular tachycardia in rats subjected to ligation of the left coronary artery. The time of onset of both initial cardiac arrhythmias and persistent ventricular tachycardia induced by aconitine infusion in mice was also significantly prolonged. These preliminary findings suggest that the ethanol extract of Sophora flavescens Ait. possesses antiarrhythmic activity.