Anisodamine (Ani) is an alkaloid first isolated in China from the root of Anisodus tanguticus. Ani 10, 15 mg.kg-1 i.v. markedly shortened the duration of arrhythmias induced by aconitine (10 micrograms.kg-1 i.v.) or by BaCl2 (2 mg.kg-1 i.v.) in anesthetized rats. Ani significantly effected on arrhythmias induced by early coronary artery ligation in rats by reducing total numbers of ectopic beats and shortening the duration of ventricular tachycardia and ventricular fibrillation 30 min after coronary ligation. The incidence of ventricular fibrillation of mice induced by chloroform were reduced from 100% to 20% and 10% by i.v. Ani 1 and 10 mg.kg-1 respectively. Ani 0.05, 0.25 mumol.L-1 prolonged the duration of neurologic refractory period of isolated guinea pig left atria and 10 mg.kg-1 i.v. had no effect on tachycardia induced by i.v. isoproterenol (0.01 mg.kg-1) but blocked the stimulation of nervi vagus. After i.v. Ani 15 mg.kg-1 P-P, P-R and QT-c intervals on the ECG were prolonged. Mean arterial pressure and diastolic pressure were reduced but systolic pressure was not effected.