Abstract: A plurality of electrodes affixed at selected positions of the chest of an ambulatory patient sense potentials due to cardiac or pacemaker action of the patient, for transmission by radio, telephone or other means to an EKG and pacemaker performance measuring and analyzing facility. The electrodes are connected to timing, control and signal processing means contained in a smal, conveniently worn or stored housing. Signals from sequenced, selected combinations of electrodes are serially transmitted for given intervals after modification, and in the case of telephone transmission are converted to audio output. The pairs of electrodes are arrayed to yield substantially all the data, from as few as four electrodes connected to provide bipolar leads, obtainable from the conventional 12 lead EKG.