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.

Midsystolic murmurs — also known as systolic ejection murmurs, or SEM — include the murmurs of aortic stenosis, pulmonic stenosis, hypertrophic obstructive cardiomyopathy and atrial septal defects. A ...

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 ...