The duration of a ventricular myocyte action potential is

The diagram depicts the relationship between the electrocardiogram (ECG) recorded on the surface of the body and the duration of a single ventricular myocyte action potential. The duration of the ventricular myocyte refractory period is nearly as long as the action potential, approximately 300 msec. The QRS complex of an ECG represents the electrical potential on the surface of the body produced by the wave of depolarization as it spreads through the ventricle and as each myocyte depolarizes (phase 0). The T wave represents ventricular repolarization (phase 3 in each myocyte). Note that the ST segment occurs during the plateau phase.