Abstract: An implantable cardiac stimulator having terminals for connections with a cardiac probe comprises an amplifier for receiving and amplifying a signal received from the probe, a band pass filter for filtering the output of the amplifier and a level detector which responds to a predetermined level of the amplified and filtered signal. A logic module comprising a clock, a microprocessor and a memory is connected with the level detector and with a magnetically operable control switch which can be actuated by a permanent magnet outside the body. The stimulator automatically performs the normal therapeutic function of palliating the patients cardiac insufficiencies and also provides means for monitoring operation of the stimulator and the condition and degree of dependency of the patient on the stimulator.