Since the introduction and development of mapping methods in clinical practice, some arrhythmias can now be treated surgically. We studied an automatized method of epicardial mapping necessitating only a single ventricular complex for the definition of epicardial activation; the signal was acquired from 35 monopolar electrodes spread out over the whole of the ventricular epicardium or concentrated in the zone of epicardial break through to localise its site more accurately. The acquisition, elaboration and tracing of these maps were performed with a computer; the activation can be presented as isochrones or isopotentials. The main value of this method of automatic mapping is the possibility of studying irregular arrhythmias whose potentials are difficult to obtain beat manually. This method has already been applied to 21 patients with ventricular tachycardia unresponsive to medical treatment and referred for surgery.