A family group of nine members was studied, two of which had W-P-W syndrome; the father type A; and the son type B. These two patients were studied from the clinical electrocardiographic and vectocardiographic point of view; and they were subject to hisian electrogram recordings. The atrial-ventricular conduction under basal conditions and during atrial stimulation is analyzed. In the first case, potential H is registered after the beginning of delta wave of the ventricular complexes in lead II. In th second case, atrial-ventricular conduction can only occur through the abnormal via (no H potential and register of delta wave in the periferial simultaneous lead), or only through the normal via (evidence of potential H with a normal H-V interval and no delta wave in the periferial line of control). The bibliography of the observation that in most family groups described up until now, there is a good correlation concerning sex. This gives the impression to be a genetic disorder linked to sex.