Abstract: A portable or implantable gastric pacemaker includes multiple electrodes that are positionable on the inner or outer surface of an organ in the gastro-intestinal tract and which are individually programmed to deliver a phased electrical stimulation to pace peristaltic movement of material through the GI tract. The pacemaker will accommodate variations in pulse amplitudes, pulse durations, pulse periods, and relative pulse phasing among the electrodes. Computer control can be used to adjust and vary all stimulation parameters delivered by the electrodes to achieve effective treatment and re-training of an organ for natural pacing. The pacemaker can be programmed with parameters to enhance or accelerate peristaltic movement through the gastric tract or to attenuate the peristaltic movement to treat such conditions eating disorders or diarrhea.