Cardiac conduction system cells have a membrane resting potential such that the outer surface of the resting cell membrane carries a positive electrical charge and the inner surface of the membrane carries a negative electrical charge. During the resting stage, the cardiac conduction system cells are polarized. The normal resting potential of the cardiac conduction system is approximately -85 to -95 millivolts (mV).
The changes in electrical potential that occur result from the movement of sodium and potassium ions across the sarcolemma of the cell. This movement of charged ions allows for the changes in electrical potential necessary to propagate the electrical charge to the next excitable cell. The movement of the sodium and potassium ions is mediated by the sodium-potassium pump.