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: Pediatrics
Loud S1 in Mitral stenosis is seen in- 
Select and explain. 
A. Prolonged flow through mitral valve, B. 1st degree hea block, C. Calcification of the valve, D. Immobilization of the valve
A: Prolonged flow through mitral valve
Answer: A: Prolonged flow through mitral valve 
Explanation: Ans. is 'a' i.e., Prolonged flow through mitral valve Siis louder in Mitral stenosis because AV flow is prolonged. The loud Si in mitral stenosis usually signifies that the mitral valve is pliable and that it remains open at the onset of isovolumetric contraction because of the elevated left atrial pressure. S1 can be soft even in the presence of mitral stenosis, when the anterior mitral leaflet is immobile and rigid due to calcification.