table1-2

Origin and features of heart sounds
Heart Sounds	Mechanism	Clinical Features
Hear a Normal Sound
First (S1)	M-T valve closure*	Single
Second (S2)	A2-P2 valve closure**	Split***
Third (S3)	Early diastole	May be normal
Fourth (S4)	Late diastole	Pathologic

Mitral and tricuspid Aortic and pulmonic **A2-P2 interval widens with inspiration.

Heart Sounds