First heart sound is loud in

(C) Mitral stenosis with friable valves # Loud S1 (Cannon sound)> Intensity of the First heart sound (S1) is influenced by: Position of the mitral leaflets at the onset of ventricular systole Rate of rise of the left ventricular pressure pulse Presence or absence of structural disease of the mitral valve Amount of tissue, air, or fluid between the heart and the stethoscope.> S1 is louder if diastole is shortened because of tachycardia, if AV flow is increased because of high cardiac output or prolonged because of mitral stenosis, or if atrial contraction precedes ventricular contraction by an unusually short interval, reflected in a short PR interval> Loud S1 in mitral stenosis usually signifies that the valve is pliable and that it remains open at the onset of isovolumetric contraction because of the elevated left atrial pressure.> A soft S1 may be due to poor conduction of sound through the chest wall, a slow rise of the left ventricular pressure pulse, a long PR interval, or imperfect closure due to reduced valve substance, as in mitral regurgitation.> Reversed splitting of the S1, in which the mitral component follows Tricuspid component, may be present in patients with severe mitral stenosis, left atrial myxoma, and left bundle branch block.