Endsystole

Endsystole refers to the final moments of ventricular systole, the phase of the cardiac cycle when the heart muscle contracts to eject blood. It is the point at which the ventricles have finished their contraction and are beginning to relax. This marks the transition from ejection to the subsequent relaxation phase, diastole.

During endsystole, the pressure within the ventricles is at its peak for that contraction cycle. The aortic and pulmonary valves, which opened at the beginning of systole to allow blood ejection, are now closing. This closure is a critical event that prevents the backflow of blood from the aorta and pulmonary artery back into the ventricles. The sound associated with this valve closure, often referred to as the second heart sound (S2), is heard during physical examination and signifies the end of systole.

The duration of endsystole is very brief, as the heart rapidly moves into the relaxation phase. This rapid relaxation, known as isovolumetric relaxation, allows ventricular pressure to fall quickly, enabling the mitral and tricuspid valves to open and refill the ventricles with blood from the atria. Understanding endsystole is important in the study of cardiac physiology and in diagnosing various cardiovascular conditions where the timing and mechanics of the cardiac cycle may be altered.