Harris tow-stage left anterior coronary ligation was performed in anesthetized dogs. After twenty hours, severe ventricular arrhythmias were recorded under conscious state. Cumulative intravenous injections of guanfu base A, a new alkaloid isolated from the tuber of Aconitum coreanum in China, from 10 to 40 mg.kg-1 produced remarkable antiarrhythmic effect lasting over 30 min and a moderate reduction of heart rate. The P-R interval, QRS complex and Q-T interval of the sinus rhythm were not significantly altered. The antiarrhythmic potency of guanfu base A in this model was found to be about one third that of quinidine.