Drug-induced arrhythmias are commonly described as proarrhythmia, arrhythmogenesis or aggravation of arrhythmias. A variety of drugs including cardiotonic drugs (antiarrhythmics, digitalis, cathecholamines), psychiatric drugs(phenothiazines, antidepressants), and macrolide antibiotics would worsen or induce arrhythmias. Among them are bradyarrhythmias and tachyarrhythmias, especially torsade de pointes(TdP) resulting from QT prolongation. There exist some predisposing factors which could potentiate proarrhythmic effect of drugs. They include age, congestive heart failure, ischemic heart disease, renal or hepatic dysfunction, electrolyte disturbance and previous history of proarrhythmia. It should be, therefore, very cautious when drugs with potentially proarrhythmic effect are given to subjects with predisposing factors. Correction of these factors and prevention of bradycardia are important in the management of proarrhythmia and TdP can be treated by infusion of magnesium.