Cardiac pacer circuit

In a demand cardiac pacemaker of the type having a source of direct current voltage, a pulse generator connected to said source of direct current voltage for periodically producing triggering pulses in the absence of normal R-wave activity in the heart, a voltage doubler capacitor and a first semiconductor switching means responsive to said triggering pulses for selectively applying artificial stimulating pulses of a given amplitude to the heart by way of electrically conductive leads and electrodes, and a sensing amplifier exhibiting a relatively high input impedance and having input terminals coupled to said electrodes by way of said leads for receiving and amplifying heart depolarizing R-wave signals, the improvement comprising:

• (a) second semiconductor switching means coupled between said electrodes and said input terminals of said sensing amplifier and third semiconductor switching means coupled between said electrodes and said voltage doubler capacitor for disconnecting said electrodes from said input terminals and for connecting said voltage doubler capacitor to said electrodes during a predetermined interval following the application of one of said triggering pulses to said first semiconductor switching means;
• and
• (b) further semiconductor switching means selectively exhibiting a low impedance for coupling said source of direct current voltage through said heart to said voltage doubling capacitor for a relatively short predetermined time following termination of said one of said triggering pulses for rapidly restoring the charge on said voltage doubling capacitor.