Preexisting anomalies of impulse formation and conduction, cardiac failure, myocardial ischemia and abnormal peripheral vasoregulation predispose the elderly patient to frequent and often severe side-effects of antiarrhythmic drugs. Paroxysmal supraventricular tachycardia in patients with sick sinus syndrome can be especially difficult to treat, as most antiarrhythmics further prolong the sinus node recovery time. Thus, implantation of a pacemaker is often necessary to prevent symptomatic bradycardia. Concomitant treatment with diuretics or digitalis also increases the risk of drug induced ventricular dysrhythmias. Interaction between quinidine, verapamil, amiodarone and digoxin may be the reason for drug toxicity. To compensate for decreased renal or metabolic drug clearances antiarrhythmic treatment in elderly patients should be initiated with lower doses than usual.