During which phase does the heart muscle receive electrical impulses to contract?

The heart muscle receives electrical impulses to contract during the phase known as electrical depolarization. This process involves the rapid influx of sodium ions through the cell membranes of cardiac muscle cells, which changes the electrical charge of the cells and triggers contraction. Depolarization is essential for the heart's function, as it initiates the cardiac cycle and allows for the synchronized contraction necessary for effective pumping of blood.

In contrast, diastole is the phase when the heart muscle relaxes and fills with blood, thus not actively contracting. Ventricular contraction refers specifically to the phase of the cardiac cycle when the ventricles are actively contracting, which occurs after depolarization. Systole, while it includes the contraction of the heart, also comprises other events and does not specifically denote the electrical activity leading to contraction. Therefore, the concept of electrical depolarization is the most precise answer, as it specifically addresses the electrical impulses responsible for initiating the subsequent contractions of the heart.