The effects of transcutaneous cardiac pacing (TCP) on cardiac activation were evaluated by endocavitary recording (HRA, RVA) in eight patients, in order to test the possibility to obtain a simultaneous atrial and ventricular stimulation. The transcutaneous pacemaker used was the Pace Aid 52 (pacing rate 50-160 ppm, current output 10-150 mA, pulse width 20 sec). The two skin electrodes (surface area 50 cm2) were placed on the chest in anteroposterior position. Ventricular capture was observed in all patients (threshold = 74 +/- 14 mA), simultaneous atrial capture was obtained in only four cases (threshold = 138 +/- 25 mA). In conclusion, our data show that four-chamber simultaneous stimulation by TCP is possible, but only with pacing energies much higher than those usually required to capture the ventricle. The ability of TCP to simultaneously pace the atria and ventricles, though not relevant in the emergency cardiac stimulation for symptomatic severe bradyarrhythmias, could be useful in the treatment of reentrant supraventricular tachycardias.