The vectorcardiograms of 5 cases of wandering pacemaker was recorded during sinus rhythm and during the various phases of the arrhythmia. The analysis of the P loops allowed us to distinguish two basic phases of the wandering pacemaker. The first phase is characterized by gradual modification of the morphology and direction of the centrifugal limb. This tends to produce an orientation of approximately zero degree in the frontal plane. The second consists of an abrupt change of direction and morphology of the whole P loop. This pattern is similar to that of nodal rhythms.