<prompt> During the cardiac cycle the opening of the aortic valve takes place at theBeginning of systoleEnd of isovolumetric contractionEnd of diastoleEnd of diastasis  <response>: Ans. b End of isovolumetric contractionRef: Ganong, 25th edp.540Isovolumetric contractionTo eject blood into aorta and pulmonary artery, ventricles must open aortic and pulmonary valveThe sole purpose of this phase is to open these valvesThe ventricle contracts against the closed valves both AV valves and semilunar valves are closedThis means that ventricular blood volume wont 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 