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 ...

Editor's Note: Before reading this article, it is recommended that readers first review "Nonauscultatory Cardiac Exam: Assessing the Elderly Person," previously published on Medscape. As with most ...

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 ...