Second Heart Sound (S2)

Second Heart Sound (S2)

Definition

S2 results from aortic and pulmonic valve closure. It is a sharper, louder sound than S1, and occurs at the end of ventricular systole.

Listening Areas

Listening Areas for S2

Heard well over the precordium; loudest at 2RICS and 2LICS.

Associated Conditions

Loud or tambour* S2:

Soft or absent S2:

 

   *sounding hollow or drum-like

See Also

Extra sounds near S2

Notes

S2 is usually louder and sharper than S1. (The popular "lub-dup" mnemonic of S1 and S2 accurately conveys this contrast in sounds.) S2 occurs at the end of ventricular systole, and is the combination of aortic (A2) and pulmonic (P2) valve closure sounds. At the end of ventricular ejection, blood flow has tapered off to the point where forward flow ceases, and then reverses itself. This reversal of flow closes the semilunar valves, causing the second heart sound. This closure sound is reflected back toward the cardiac base, where S2 is louder than S1.

When the aortic and pulmonic valves close asynchronously, the sound is called split S2. Note however, that the opening snap of mitral stenosis occurs shortly after S2, and the S2-OS combination may be confused with a truly split S2. An S2-S3 combination may also be confused with split S2.