What occurs during systole in the heart?

During systole, the key event is the contraction of the ventricles, which generates the pressure necessary to eject blood into the systemic circulation (via the aorta) and into the pulmonary circulation (via the pulmonary arteries). This process involves the closure of atrioventricular valves (the mitral and tricuspid valves) to prevent backflow into the atria, allowing the ventricles to contract effectively and push the blood out into the arteries.

The closure of the valves is critical because it creates the high pressure in the ventricles that is necessary for the ejection of blood. This is also when the heart sounds (the "lub" or first heart sound) are produced due to the closure of these valves.

In contrast, atrial contraction typically occurs during diastole rather than during systole, when the heart is filling with blood, and blood flow from the aorta to the body is a consequence of ventricular contraction rather than a defining feature of the systole phase itself. Therefore, focusing on the mechanics of ventricular contraction and valve closure accurately describes the actions that characterize systolic function.