Abstract: An implantable medical device comprises a control circuit and a memory. The memory is operably coupled to the control circuit. The memory comprises instructions that, when executed by the control circuit, cause the control circuit to monitor an output of at least one comparator, the output of the at least one comparator being responsive to a cardiac signal of a patient. The instructions further cause the control circuit to automatically adjust a gain level applied to the cardiac signal over time based on the monitored output of the at least one comparator.