Heart Sounds S1 and S2: "Lubb‑Dup" Explained

First Heart Sound (S1 – "Lubb")

Closure of mitral and tricuspid valves at the onset of ventricular systole. Best heard at the apex (mitral area). Signifies start of ejection.

Second Heart Sound (S2 – "Dup")

Closure of aortic and pulmonary valves at the end of systole. Best heard at the base (aortic/pulmonic areas). Signifies end of ejection and start of diastole.

Clinical Pearls

• Splitting of S2 varies with respiration (physiologic).
• Loud S1: mitral stenosis; soft S1: long PR, severe MR.
• Loud P2: pulmonary hypertension.