Repolarization is the process whereby the transmembrane voltage changes from its value at the end of rapid depolarization of approximately +30 mV to its diastolic value of -85 mV. Repolarization consists of the plateau and downstroke of the action potential. The components of the action potential have been assigned numerical labels as follows: the rapid upstroke is referred to as phase 0, the spike of the action potential is phase 1, the plateau is referred to as phase 2 and the downstroke is referred to as phase 3. The diastolic phase, when the trans-membrane potential is at its resting level, is referred to as phase 4