type pacer in this instance the capture detect signal is communicated to auto threshold logic 61 auto threshold logic 61 controls the energy content of the pacing pulses delivered by the output circuit 68 to the lead system via capacitor 74 in the event that a pacing pulse is delivered and no capture detect signal follows auto threshold logic 61 will generate a control signal allowing input output circuit 30 to increment the amplitude of the pacing pulses provided by output circuit 68 auto threshold logic 61 may also decrement the amplitude of the pacing pulses in response to an extended period in which all pacing pulses successfully capture the heart to enable a determination of the minimum energy required to reliably pace the heart auto threshold logic 61 may also respond to the failure of a pacing pulse to capture the heart by quickly triggering an additional pacing pulse at an increased amplitude appropriate mechanisms for adjusting the energy content of the pacing pulses generated by output circuit 68 are disclosed in u s pat no 4 858 610 issued to callaghan et al u s pat no 4 878 497 issued to callaghan et al and u s pat no 4 729 376 issued to decote all of which are incorporated herein by reference in their entireties alternative pacing functions which may be modified in response to the detection or nondetection of cardiac depolarizations during the capture detect window are described in u s pat no 4 759 366 issued to callaghan et al and in the above cited u s pat no 4 305 396 issued to whittkampf both of which are incorporated herein by reference in their entireties the operation.