Abstract: An auxiliary rotary selector switch is provided, preferably conveniently near a standard single-channel ECG instrument. The V lead of the instrument is connected to one end of the center conductor of a coaxial cable, the opposite end of which is connected to the center contact of the auxiliary switch. Each of several stationary switch contacts is connected to a conductor of an auxiliary patient cable, the opposite ends of the conductor being attached to a corresponding number of V electrodes spaced across the chest of the patient. By oscillating the center contact, separate V readings, one for each of the chest electrodes may be recorded. The extender is actually connected to the ECG instrument when the selector switch of that instrument is turned to the V lead position, and the signals from the plural V electrodes are recorded serially on the chart as the auxiliary selector switch is turned.