Abstract: Pretreatment of rats with sinomenine 10～20 mg/kg iv significantly delayed the appearence and reduced the percentage of arrhythmia induced by aconitine 20 μg/kg iv. This alkaloid given 20 mg/kg iv increased the amount of ouabain required to produce ventricular premature beats and cardiac arrest in guinea pigs. while 20 mg/kg ip significantly reduced the incidence of ventricular fibrillation induced by chloroform inhalation in mice. In aneasthetized rats, sinomenine 20 mg/kg iv reduced the incidence of ventricular fibrillation and the mortality rate induced by iv CaCl₂ 130 mg/kg. It might also abolish the arrhythmia induced by chloroform-adrenaline in rabbits.