What process occurs just before the ventricles contract?

Just before the ventricles contract, the process known as isovolumetric contraction occurs. During this phase, the ventricles are filled with blood and the pressure within them rises as the cardiac muscle fibers contract. However, during isovolumetric contraction, all heart valves are closed, which means that no blood is ejected from the ventricles yet. This is a crucial phase of the cardiac cycle because it helps build the pressure necessary to open the aortic and pulmonary valves for the eventual ejection of blood.

The other processes mentioned, such as atrial systole and ventricular filling, occur earlier in the cardiac cycle. Atrial systole is the phase where the atria contract to push blood into the ventricles, which is completed before the ventricles begin their contraction. Ventricular filling happens during diastole when the ventricles are relaxing, and the heart is receiving blood from the atria. Ventricular ejection follows contraction, making it a subsequent phase rather than one occurring just before the ventricles contract. Understanding the order and significance of these phases is key in grasping heart physiology.