Cardiac monitoring apparatus and monitor

Cardiac monitoring apparatus comprising a first external unit for transmitting electromagnetic energy within the patient's body to be received by a second, surgically implanted unit within the patient's body and adapted to be solely powered by the transmitted electromagnetic energy. The internal unit includes a monitoring circuit connected via electrodes coupled to first and second sites of the patient's heart, for providing corresponding first and second signals to be first time multiplexed and then pulse-width modulated before being re-transmitted to the external unit. The external unit decodes the transmitted signals to provide diagnostic quality signals indicative of the patient's EKG.