A cardiac pacer system includes a pulse generator for generating a stimulating signal coupled through an output coupling capacitor to a single heart-engaging electrode. An amplifier is coupled to the electrode for sensing an R wave. Immediately upon initiation of the stimulating pulse, a discharging resistor for the coupling capacitor is disconnected, and the signal input to the amplifier is uncoupled from the electrode. The amplifier is restrained and its gain is reduced. When the stimulating pulse terminates, the input terminal of the output coupling capacitor is clamped through resistance to ground and discharged rapidly. The current discharging the output coupling capacitor assists in discharging the electrode capacitance. During amplifier restraint, the amplifier input coupling capacitor is allowed to charge to a voltage sufficient to compensate for the voltage offset on the system output coupling capacitor and the electrode capacitance. The output coupling capacitor's discharging current is interrupted when the rate of change of voltage at the output coupling capacitor and electrode will, in a short length of time, reach a value nearly equal to zero; and the voltage offset is compensated. After sensing, the discharging resistor is reconnected, and the gain of the amplifier is returned to its original value.