This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
During the cardiac cycle the opening of the aortic valve takes place at the 
Select and explain. 
A. Beginning of systole, B. End of isovolumetric contraction, C. End of diastole, D. End of diastasis
B: End of isovolumetric contraction
Answer: B: End of isovolumetric contraction 
Explanation: Ans. (b) End of isovolumetric contractionRef: Ganong, 25th ed/p.540Isovolumetric contraction#To eject blood into aorta and pulmonary artery, ventricles must open aortic and pulmonary valve#The sole purpose of this phase is to open these valves#The ventricle contracts against the closed valves (both AV valves and semilunar valves are closed)#This means that ventricular blood volume won't change (isovolumetric) but the pressure generated by the ventricle tremendously rises.#Once the pressure rises above 80 mm Hg, aortic valve opens. Similar changes also happen in right ventricle which opens the pulmonary valve