Final answer:
Ejection of blood from the left ventricle occurs when the left ventricular pressure exceeds aortic pressure, with the aortic semilunar valve open, allowing blood to be ejected into the aorta during the ventricular ejection phase of systole.
Therefore, Option A is correct.
Step-by-step explanation:
Ejection of blood from the left ventricle occurs when pressure in the left ventricle exceeds pressure in the aorta, when the aortic semilunar valve is open. This happens during the second phase of ventricular systole, known as the ventricular ejection phase. In this phase, the ventricles contract and increase the pressure within to higher than that in the aorta and pulmonary trunk, which allows blood to be ejected from the heart. The left ventricle is the main pumping chamber for the systemic circuit and successfully pumps blood into the aorta through the open aortic semilunar valve.
Furthermore, the stroke volume, which is the amount of blood pumped by each ventricle during a single heartbeat, is generally in the range of 70-80 mL. After the ventricular ejection, there is 50-60 mL of blood remaining in the ventricle, known as the end systolic volume (ESV). During ventricular diastole, as the ventricles relax, the pressure within them falls. Once it falls below that of the pulmonary trunk and aorta, the semilunar valves close to prevent backflow into the heart, marking the beginning of the isovolumic ventricular relaxation phase.