Although the efficacy of verapamil in the treatment of paroxysmal supraventricular tachycardia is well established,1-4 most of these studies refer to intravenous administration or short-term oral therapy. Since follow-up data on long-term oral prophylaxis are lacking, we have undertaken a study to assess the long-term efficacy of verapamil in the prevention of paroxysmal supraventricular t,achycardias. We selected 56 consecutive patients with chronic recurrent (more than once-daily attacks) paroxysmal supraventricular tachycardia, in whom pretreatment with drugs such as digitalis, beta blockers, quinidine, disopyramide, and other antiarrhythmics had to be discontinued because of ineffectiveness (42 patients) or undesirable side effects (14 patients). All 56 patients responded to short-term (4 weeks) oral therapy with verapamil, continued their longterm medication, and could be followed up for at least 1 year. Of those 56 patients, 20 had paroxysmal atrioventricular junctional tachycardia, 9 had circus movement tachycardias in association with the Wolff-ParkinsonWhite (WPW) syndrome, since programmed electrical stimulation revealed that an acessory pathway was used in a ventriculoatrial direction ,5 24 had paroxysmal atria1 fibrillation or flutter, and 3 had paroxysmal atrial tachycardia. Their ages varied from 10 to 83 years (mean 52 years). Organic heart disease was present in 14, with coronary artery disease being the most frequent (8 patients). The dosage of long-term oral treatment varied from 120 to 320 mg, and the follow-up period ranged from 12 to 48 months (mean 25.4 months). Twenty-five patients were asymptomatic, whereas Holter monitoring showed no episodes of supraventricular tachycardia. The remaining 31 patients noticed a marked reduction of symptoms to at