1.9.5 Ventricular Ejection Definition

Ventricular Ejection Definition is the phase of ventricular systole during which blood is actively expelled from the ventricles into the aorta and pulmonary artery. This phase begins the instant intraventricular pressure exceeds the pressure within the great vessels, causing the semilunar valves to open, and it ends when ventricular pressure falls below arterial pressure, causing those valves to close. Ventricular ejection follows isovolumetric contraction and represents the only portion of the cardiac cycle during which forward flow of blood out of the ventricles occurs.

Subphases of Ejection

Ventricular ejection is not uniform in velocity or volume throughout its duration; it is classically divided into two consecutive stages.

Rapid Ejection

Rapid ejection occurs immediately after the semilunar valves open, when the pressure gradient between the ventricle and the corresponding great vessel is greatest. During this stage, the majority of the stroke volume, often more than two-thirds, is expelled in a short interval.

Reduced Ejection

Reduced ejection follows as ventricular contraction begins to wane and the pressure gradient diminishes. Blood continues to flow out of the ventricle, but at a progressively slower rate, until ventricular pressure falls below arterial pressure and the semilunar valves close, terminating ejection.

Valve Behavior

The opening and closing of the semilunar valves define the temporal boundaries of ventricular ejection.

Aortic Valve

The aortic valve opens when left ventricular pressure exceeds aortic pressure and closes when left ventricular pressure falls below aortic pressure, the latter event producing the second heart sound (S2).

Pulmonary Valve

The pulmonary valve behaves analogously on the right side of the heart, opening when right ventricular pressure exceeds pulmonary arterial pressure and closing as that pressure gradient reverses.

Volume Changes

Ejection reduces ventricular volume from its maximum, the end-diastolic volume, to its minimum, the end-systolic volume.

Stroke Volume

The volume of blood ejected during this phase constitutes the stroke volume.

Ejection Fraction

The proportion of end-diastolic volume that is ejected is termed the ejection fraction, a key clinical index of ventricular systolic function.

Pressure Dynamics During Ejection

Arterial and ventricular pressures rise together during rapid ejection, reach a shared peak, and then decline together during reduced ejection as ventricular contraction weakens, until the reversal of the pressure gradient closes the semilunar valves.

Diagrammatic Summary

Physiological Significance

Ventricular ejection is the mechanical event responsible for generating the arterial pulse and delivering cardiac output to the systemic and pulmonary circulations. Impaired ejection, whether from reduced myocardial contractility, excessive afterload, or valvular obstruction, directly lowers stroke volume and ejection fraction and is central to the pathophysiology of systolic heart failure.