What is happening to the heart during systole?

As a cardiac physiologist with a focus on the mechanics of the heart, I can explain the process of systole in detail. Systole refers to the phase of the cardiac cycle during which the heart contracts and pumps blood out into the circulatory system. This process can be broken down into two parts: atrial systole and ventricular systole. During atrial systole, the atria (the upper chambers of the heart) contract. This contraction forces the remaining blood from the atria into the ventricles (the lower chambers of the heart) through the atrioventricular valves, which are the tricuspid valve on the right side and the mitral valve on the left side. Following atrial systole, ventricular systole occurs. This is the more powerful contraction that involves the ventricles. The process can be further divided into several stages: 1. Isometric Contraction: The ventricular muscle fibers contract, but the pressure inside the ventricles has not yet surpassed the pressure in the arteries, so the valves remain closed. 2. Ejection Phase: Once the ventricular pressure exceeds the arterial pressure, the aortic and pulmonary valves open, and blood is ejected from the left ventricle into the aorta and from the right ventricle into the pulmonary artery. 3. Isometric Relaxation: As the contraction of the ventricles begins to decrease, the pressure inside the ventricles falls below the pressure in the arteries, causing the aortic and pulmonary valves to close. 4. Filling Phase: The ventricles relax and begin to fill with blood again in preparation for the next contraction. The entire process ensures that oxygenated blood is circulated to the body and deoxygenated blood is sent to the lungs for reoxygenation.

During systole the thick muscular walls of the ventricles contract. This happens to both sides of the heart at about the same time. The diagram shows systole in the left side of the heart. The contraction of the ventricular muscle raises the pressure in the ventricle.