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
Which point on the diagram marks the beginning of ventricular systole? 
Select and explain. 
A. A, B. B, C. C, D. D
A: A
Answer: A: A 
Explanation: Ans. A. APressure - volume loop of the left ventricle. During diastole, the ventricle fills and pressure increases from d to a. Pressure then rises sharply from a to b during isovolumetric contraction and from b to c during ventricular ejection. At c, the aortic valves close and pressure falls during isovolumetric relaxation from c back to d.Isovolumetric contraction starts at A therefore it is the beginning of ventricular systole.