Abstract: The effects of sophoramine on experimental arrhythmias in animals and its mechanisms were studied. Sopaoramine is an alkaloid isolated from Sophora alopecuroides L. The iv and ip LD₅₀ of sophoramine in mice were found to be 74.90+17.86 and 106.15+1.05 mg/kg respectively.Sophoramine showed significant effects on arrhythmias induced by aconitine, BaCl₂ and CaCl₂ in rats, CHCl₃ in mice and CHCl₃—adrenatine in rabbits.The ECG of ansthetized rats was significantly changed after intravenous injection of sophoramine. The RR and PR intervals were prolonged. The tachycardia induced by intravenous injection of isoprenalne was depressed but the tachycardia induced by atropine was not. In in vitro experiments, the effective refractory period (ERP) of isolated rabbit left atria was prolonged by the addition of sophoramine.Sophoramine showed negative automaticity action, negative chronotropie action, and negative conduction and prolonged the ERP. These actions of sophoramine may e the pharmacological basis for antiarrhythmia.