The first heart sound, or S1, is the "lub" of a normal heartbeat. It's a high-pitched sound that occurs at the beginning of ...

The second heart sound (S2) is produced by the closure of the aortic and pulmonic valves. The sound produced by the closure of the aortic valve is termed A2, and the sound produced by the closure of ...

The S3 heart sound occurs as the mitral valve opens and allows blood to fill the left ventricle passively. The sound happens as a result of blood striking the left ventricle during early diastole. An ...