Abstract: A recording device using a portable recorder, such as a small, battery powered tape recorder, carried on the person and provided with electrodes for attachment to the body of the user, the electrodes being operable to sense cardiac activity and to provide the input signals to a program module coupled with the recorder to cause the latter to be turned on and off at predetermined times so that it operates at predetermined periods for the purpose of recording samples of the user's cardiac activity sensed by the electrodes. The program module operates to amplify the input signals from the electrodes and to cause these signals to modulate a carrier wave signal suitable for recording by the tape or other recorder. The program module also is operable to demodulate the carrier wave signal when it is played back from the recorder to reproduce an accurate reproduction of the input signals from the electrodes.