• Major electrolytes that influence cardiac function are calcium, potassium, sodium, and magnesium
– Electrical charge (potential difference) between inside and outside of cells is expressed in millivolts
– When cell is in resting state, electrical charge difference is referred to as resting membrane potential
– Specialized sodium–potassium exchange pump actively pumps sodium ions out of cell, also pumps potassium ions into cell
– Cell membrane appears to have individual protein‐lined channels, which allow for passage of specific ion or group of ions