Final answer:
Phase 3, Ventricular Ejection, during Ventricular Systole, consists of isovolumic contraction and the ventricular ejection phase. Blood pressure rises until the semilunar valves open, allowing ejection of blood, wherein the stroke volume is pumped from the heart and the remaining is the ESV.
Step-by-step explanation:
Phase 3 of the cardiac cycle, known as Ventricular Ejection, occurs during Ventricular Systole which is when the ventricles contract. This phase can be subdivided into two parts: isovolumic contraction and the ventricular ejection phase. During isovolumic contraction, the pressure in the ventricles rises, closing the tricuspid and mitral valves but not yet opening the pulmonary and aortic semilunar valves, leading to a phase where blood volume in the ventricles remains constant. In the ventricular ejection phase, the pressure becomes high enough to open the semilunar valves, and blood is expelled from the heart into the pulmonary trunk and the aorta.
The end diastolic volume (EDV) or preload is the amount of blood in the ventricles just before contraction, usually about 130 mL. After the contraction, the remaining blood volume, called the end systolic volume (ESV), is typically 50-60 mL. The difference between EDV and ESV, usually between 70-80 mL, is known as the stroke volume.