A simple and inexpensive method of monitoring the movement of an isolated frog heart provides comparable results to those obtained with a force transducer. A commercially available photoresistor is integrated into a Wheatstone bridge circuit, and the output signal is interfaced directly with a recording device. An excised, beating frog heart is placed in a Petri dish and over the photoresistor so that movements produced during the heartbeat cycle change the amount of light entering the photoresistor and, therefore, the voltage output from the circuit. Experiments that can be done with this system include the effects of temperature and dose-response relationships with Ringer's solutions containing acetylcholine and norepinephrine.