Electromagnetic radiation is being used to inactivate the enzymes at specific times during the beat cycle of the spontaneously beating turtle heart. ECG and reflectrometry is used to monitor events in the beat. After inactivation of the enzymes, the following compounds are assayed: in the right auricle, left auricle, ventricular apex, ventricular base, acetylcholine, choline, cyclic AMP and GMP, the high energy phosphates, lactate and pyruvate.