Slow gain control

A system and method automatically controls a gain of a cardioverter/defibrillator which receives electrical activity of the heart and delivers shock pulses in response thereto. An amplifier amplifies the electrical activity according to a variable gain. A detection circuit detects depolarizations in the amplified electrical activity and provides a detect signal representing a cardiac event indicative of a depolarization when the amplified electrical activity exceeds a sensitivity threshold. A storage device stores peak history information representative of peak values of the amplified electrical activity of a first selected number (N) of cardiac events. Slow gain control circuitry adjusts the variable gain in discrete steps based on the stored peak history information.