This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which heart sound indicates stiffness of ventricular wall 
Select and explain. 
A. S1, B. S2, C. S3, D. S4
D: S4
Answer: D: S4 
Explanation: If S4 is heard as a result of stiffness of ventricular walls, as relaxation is impaired due to decreased ATP (as blood flow to heart is decreased).