Lub Dub Heart Sounds

| Feature | | S2 ("Dub") | | :--- | :--- | :--- | | When it occurs | Beginning of systole (ventricular contraction) | Beginning of diastole (ventricular relaxation) | | Which valves close? | Atrioventricular (AV) valves (Mitral & Tricuspid) | Semilunar (SL) valves (Aortic & Pulmonic) | | Location of sound | Loudest at apex of heart (5th intercostal space, midclavicular line) | Loudest at base of heart (2nd intercostal space, right & left sternal border) | | Pitch | Slightly lower, longer | Slightly higher, shorter | | Timing relative to pulse | Occurs just before the carotid pulse | Occurs just after the carotid pulse |

While "lub-dub" is the standard, doctors often listen for subtle additions that tell a deeper story: Chapter 9 Cardiovascular Assessment - Nursing Skills - NCBI lub dub heart sounds