Heart Sounds

The first heart sound (S1) is caused by closure of the mitral and tricuspid valves whilst the second heart sound (S2) is due to aortic and pulmonary valve closure

S1

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

S2

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

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

S4 (fourth heart sound)

• may be heard in aortic stenosis, HOCM, hypertension