This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiac Cycle, Subject name: Physiology
'Y' descent in the JVP is due to: 
Select and explain. 
A. Atrial diastole, B. Closure of the tricuspid valve, C. Opening of the tricuspid valve, D. Isovolumetric relaxation of right ventricle
C: Opening of the tricuspid valve
Answer: C: Opening of the tricuspid valve 
Explanation: "y" wave indicates fall of right atrial pressure due to opening of tricuspid valve leading to ventricular filing.