A new method for pacemaker treatment of refractory reentry tachycardias has been developed which in 5 patients proved effective over a period of up to ten months. The system consists of a modified QRS-synchronous pacemaker and an external trigger unit. During tachycardia the external unit senses pacemaker spikes and by timed skin stimulation activates the implanted pacemaker to provoke the ventricular premature beats necessary for interruption of the tachycardia. The system also allows repetitive non-invasive programmed stimulation of the heart.