A third heart sound, or S3, is a low-frequency, extra heart sound that may be heard with a stethoscope right after the normal S1 and S2 heart sounds. S1 and S2 are the "lub-dub" sounds of a heartbeat ...

The first heart sound (S1) results from the closing of the mitral and tricuspid valves. The sound produced by the closure of the mitral valve is termed M1, and the sound produced by closure of the ...

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 ...