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 systole—when the heart pumps blood out of the heart into the lungs or body.

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 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 ...

An S4 heart sound cannot be present during atrial fibrillation (atrial kick is required). An S3 heart sound cannot be present in the setting of severe mitral stenosis. An S3 heart sound can be present ...

Pulmonary Circulation, Vol. 4, No. 4 (December 2014), pp. 685-695 (11 pages) AbstractWe studied digital stethoscope recordings in children undergoing simultaneous catheterization of the pulmonary ...