Abstract: One embodiment of the present invention is a mode switching method and apparatus for an external, dual chamber cardiac pacemaker having multiple single chamber and dual chamber primary pacing modes and user adjustable atrial and ventricular sensitivities. The dual chamber demand pacing mode, e.ga. the DDD or DDI mode, is in effect as long as the atrial and ventricular pace pulse amplitudes are set by the user within an operative range. The pacing mode is switched to a single chamber demand mode when one of the atrial and ventricular pace pulse energies is set to an inoperative setting which preferably is a no output setting. If the atrial pace pulse amplitude is set to no output, then the mode is switched to a single chamber demand mode with ventricular sensing and pacing, preferably the VVI mode. If the ventricular pace pulse amplitude is set to no output, then the mode is switched to a single chamber mode with atrial sensing and pacing, preferably the AAI mode.