<prompt> Loud S1 in Mitral stenosis is caused by:Prolonged flow through mitral valve1st degree hea blockCalcification of the valveImmobilization of valve  <response>: Answer is A Prolonged flow through mitral valve Loud SI in mitral stenosis results from prolonged AV flow through the mitral vain S1 is louder i fAV flow is prolonged because of mitral stenosis -- Harrison Reduced mobility of valve Immobility, calcification, and Prolonged PR interval 1st degree block are all causes of soft S1. Note: First degree block is characterized by prolonged PR interval. 