Which of the following accurately describes the contraction phase of the ventricles?

The contraction phase of the ventricles is known as systole. During this phase, the ventricular muscles contract to pump blood out of the heart. Specifically, the right ventricle ejects blood into the pulmonary artery, while the left ventricle sends blood into the aorta. This contraction is triggered by electrical impulses from the heart's conduction system, resulting in the coordinated and powerful contraction necessary for effective circulation.

In contrast, diastole refers to the relaxation phase, where the ventricles fill with blood. Mid-diastole describes an intermediary phase within diastole, primarily focused on the filling process. End-systole marks the conclusion of the systolic phase, when the ventricles have completed their contraction, but it is not an accurate descriptor of the contraction process itself. Hence, systole is the term that best captures the active contraction of the ventricles.