affixed over bony portions of the body of the patient and thus are not subject to sensing irregular potentials due to muscular artifacts which obscure sometimes to a considerable degree the cardiac data desired the electrodes are placed on the patient 39 s body so that they are conveniently accessible to the patient as shown in fig7 a the electrodes are connected to signal processing means 32 which amplifies and otherwise prepares electrical currents due to the potentials sensed by the electrodes for transmission to a distant facility having the capability of graphing and analyzing the cardiac data from the patient the signal processing means 32 has very high impedance in relation to the impedance of the patient typically 2 000 megohms at 1 cps and 500 megohms or more at 120 cps as compared with 150 000 ohms or less for the patient thus variations in skin resistance of the patient have little or no effect on the graphical record of the patient 39 s cardiac data control means 34 is connected to the signal processing means 32 and provides signals to the signal processing means 32 so that the means 32 is conductive with respect to selected pairs of electrodes for selected time intervals and in a chosen sequence to form a complete cycle for multiplex transmission for example a practical sequence is lead i second electrode minus first electrode lead iii third electrode minus second electrode lead cm 5 third electrode minus first electrode and v 1 lead fourth electrode minus second electrode a dc power source 36 in the form of a battery is coupled to the signal processing means 32 at a preselected point in the multiplex cycle the control means 34 provides a signal activating sync or battery test means 37.