Loud S1 Causes [upd] -

The first heart sound (S1) is produced primarily by the closure of the mitral and tricuspid valves at the onset of ventricular systole. A loud S1 indicates that the valve leaflets are closing from a wider distance or with greater force than normal. While it can be a normal finding in thin-chested individuals, a pathologically loud S1 is a valuable clinical clue.