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
First hea sound is soft in all, except: 
Select and explain. 
A. Sho PR interval, B. Ventricular septal defect, C. Mitral regurgitation, D. Calcified valve
A: Sho PR interval
Answer: A: Sho PR interval 
Explanation: Answer is A (Sho PR interval) Sho PR interval is associated with a Loud S,. SI is produced as a result of closure of AV valves. In sho PR interval mitral leaflets are at a greater distance from neutral as decreased interval between atrial contraction and ventricular systole does not allow them to return towards neutral before the ventricular contraction