S1

• closure of mitral and tricuspid valves
• soft if long PR or mitral regurgitation
• loud in mitral stenosis

Wide splitting of S1 that is accentuated by inspiration is a sign of delayed closure of the tricuspid valve. This condition can occur in patients with complete RBBB or tricuspid stenosis.

Variable intensity of S1 in complete heart block (CHB)

• S1 intensity decreases with PR interval prolongation, as diastolic filling pressures in the left ventricle increase and cause the mitral valve leaflets to drift together. Hence, the variation in PR interval seen in CHB causes variation in S1 intensity.

Heart Sound - S2

• closure of aortic and pulmonary valves
• soft in aortic stenosis
• splitting during inspiration is normal

Heart Sound - S3

S3 (third heart sound)

• caused by diastolic filling of the ventricle
• considered normal if < 30 years old (may persist in women up to 50 years old)
• heard in left ventricular failure (e.g. dilated cardiomyopathy), constrictive pericarditis (called a pericardial knock) and mitral regurgitation

Heart Sound - S4