Final answer:
Phase 4 of the ventricular action potential coincides with diastole, which is the period of heart muscle relaxation and chamber filling. The correct option is E).
Step-by-step explanation:
The phase of the ventricular action potential that coincides with diastole is Phase 4. Diastole refers to the period when the heart muscle relaxes and the chambers fill with blood.
During this phase, the ventricular action potential returns to its resting state, just after the repolarization that occurs in Phase 3 and before the next atrial depolarization.
Ventricular diastole is seen on the ECG as the T wave, which corresponds to ventricular repolarization, followed by a return to the isoelectric baseline representing the state of the heart's electrical system during diastole (Phase 4). Option E) is the correct one.