Which of the following events occurs during ventricular systole?

During ventricular systole, the primary event is the contraction of the ventricles, which generates the pressure necessary to eject blood into the arteries. At the onset of this phase, the atrioventricular (AV) valves close to prevent the backflow of blood into the atria. This closure is crucial for maintaining the direction of blood flow as the ventricles contract; it ensures that blood is pushed forward into the pulmonary artery and the aorta rather than flowing backwards into the atria.

The closing of the AV valves also marks the beginning of ventricular contraction and is responsible for the first heart sound, often referred to as "lub." This process is a vital part of the cardiac cycle and underscores the importance of directional blood flow through the heart's chambers.