S1 - First Heart Sound

Produced by:	Closure of atrio-ventricular valves
Auscultation	Diaphragm. 'LUB dup'
Intensity	HR, CO, MS, short P-R interval (more common).
Intensity	obesity, MR, long P-R interval.
Normal Splitting	M1 --- T1 (10 to 30 msec). 'T-LUB dup'
Widened Splitting	M1 ------ T1 (complete RBBB).
Reversed Splitting	T1 --- M1 (severe MS, complete LBBB).
Comments	avoid confusing it with the opening snap.