The effect of mgSO4 on epinephrine-induced arrhythmia were evaluated in twenty male rabbits anesthetized with halothane. Epinephrine was given intravenously at a rate of 5 mcg/Kg/min by a constant volume infusion pump until two or more premature ventricular contractions occured. The arrhythmogenic dose of epinephrine was determined to be the dose at which the onset of arrhythmia occured. Thirty seconds after the onset of arrhythmia, either mgSO4 8mg/kg(group 1, n=10) or lidocaine 1.5mg/kg(group 2, n=10) was injected and repeated at 30 second intervals up to 4 times until normal sinus rhythm returned. Intravenous injection of mgSO4 decreased the duration of arrhythmia. The arrhythmia duration of group 1(78.5±23.9 sec) was shorter than group 2(92.5±46.1 sec) but which was statistically insignificant. Two cases of group 1 and four cases of group 2 did not treated by antiarrhythmic agents, but there were not statistically significant. The results of this study show that compared to lidocaine, mgSO4, had a shorter duration of epinephrine-induced cardiac tachyarrhythmia although it was not statistically significant. However malignant ventricular tachyarrhythmia not controllable with lidocaine and other conventional drugs, mgSO4 infusion is recommended.