The closing of the mitral valve and the tricuspid valve constitutes the first heart sound ( S1 ).
2.
As the ventricular systole begins, pressure within the ventricle rises and the AV valve closes producing the'first heart sound'( S 1 ).
3.
The first heart sound may be followed by a sharp ejection sound ( " ejection click " ) best heard at the lower left sternal border and the apex, and, thus, appear to be " split ".
4.
Findings on clinical examination depend on the severity and duration of MI . The mitral component of the first heart sound is usually soft and with a laterally displaced apex beat, often with P 2, heard best when lying on the left side.
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