Atropine (Atr) ip 5 - 10mg/kg elevated the threshold dose of ouabain ( 10?g/min, iv ) to induce ventricular premature beats, ventricular tachycardia , ventricular fibrillation and cardiac arrest in guinea-pigs. Atr 2 - 4 mg/kg iv shortened the duration of arrhythmia elicited by Adr ( 40?g/kg, iv ) in conscious rabbits, & delayed the onset of arrhythmia evoked by AC ( 20?g/kg, iv ) or BaCl2 ( 2mg/kg, iv ) in anesthetized rats. It also decreased the incidence of arrhythmia induced by CaCl2 ( 102mg/kg, iv ) in rats. In mice, Atr ( 5~10mg/kg, ip)decreased the incidence of ventricular fibrillation by chloroform and artrial fibrill-ation ( or flutter ) by Ach-CaCl2.