Pay attention: Notice in S1 that when the tricuspid and mitral valve close, the heart is ejecting blood through the OPEN aortic and pulmonic valve. In S2, the aortic and pulmonic valves are closed and the tricuspid and mitral valves are OPEN to fill the ventricles. Take a moment to look at the pictures and think!

The Extra Heart Sounds

The S3 and S4 sounds are best heard with the bell-side of the stethoscope at the apex of the heart.
S3: Third heart sound also called a ventricular gallop. It is caused by Rapid ventricular filling. It occurs at the beginning of diastole after S2. The third heart sound may be benign. The most common abnormal causes are left ventricular failure, fluid overload, and mitral regurgitation.
S4: Fourth heart sound also called a atrial gallop. This gallop is produced by the sound of blood being actively forced into a stiff/hypertrophic ventricle. It is almost always pathological. It is due to left ventriclular hypertrophy, hypertension, or aortic stenosis.

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