This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
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: Ref Harrison 19 th ed pg 1447 S1 becomes softer in the later stages of MS when the leaflets are rigid and calcified, after exposure to b-adrenergic receptor blockers, with long PR intervals, and with left ventricular contractile dysfunc- tion. The intensity of hea sounds, however, can be reduced by any process that increases the distance between the stethoscope and the responsible cardiac event, including mechanical ventilation, obstruc- tive lung disease, obesity, pneumothorax, and a pericardial effusion.