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 anesthetized rats was significantly changed after intravenous injection of sophoramine. The RR and PR intervals were prolonged. The tachycardia induced by intravenous injection of isoprenaline 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 chronotropic action, and negative conduction and prolonged the ERP. These actions of sophoramine may be the pharmacological basis for anti-arrhythmia.