The efficacy of noninvasive transcutaneous cardiac pacing (TCP) in the treatment of tachyarrhythmic events was tested in 24 patients: 14 with ventricular tachycardia, seven with supraventricular tachycardia and three with atrial flutter. Six (42.9%) ventricular tachycardias were interrupted: in two of the ten patients on whom underdrive pacing was attempted and in all four cases in which overdrive stimulation was possible. Five of the six supraventricuiar tachycardias utilizing an atrioventricular bypass tract were interrupted, while the TCP was unsuccessful on the only patient with atrioventricular nodal reentrant tachycardia. TCP failed to interrupt the arrhythmia in the three cases of atrial gutter. No clinically significant untoward effects (in particular tachycardia acceleration or ventricular fibrillation) were observed, except for a tolerable thumping sensation on the chest during pacing. In four patients, TCP effects on cardiac activation was evaluated by endocavitary recording: while the mean ventricular threshold was 70 mA, atrial capture was possible on only two patients at a current intensity of 140 and 150 mA. We consider our preliminary experience with TCP in the treatment of tachycardias encouraging. The technique was easily and rapidly usable and it was immediately successful in the majority of atrioventricular reentrant tachycardias and in a relevant percentage of ventricular tachycardias. In this latter setting TCP was mostly effective in the slower tachycardias where overdrive pacing was possible. A further experience with devices provided by higher pacing rales is warranted.