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 |

| | | S2 (Dub) | |--|-------------|-------------| | Phase | Systole | Diastole | | Valves | Mitral + Tricuspid | Aortic + Pulmonic | | Pulse relation | Before pulse | After pulse | | Loudest at | Apex | Base | | Split on inspiration? | No | Yes (normally) |

The characteristic "lub-dub" rhythm represents the fundamental cycle of a beating heart, with each sound marking a critical mechanical event. Often described as , these sounds are the primary focus of cardiac auscultation—the process of listening to the heart through a stethoscope. The "Lub" (First Heart Sound - S1)

The second heart sound, or S2, marks the end of systole and the beginning of diastole (the relaxation phase). It is produced by the closure of the :

While S1 and S2 are normal, the presence of S3 or S4 indicates pathology.

: Ventricles relax as the heart prepares to refill (diastole). Interesting "Extra" Sounds

The splitting of S2 is a crucial concept in understanding cardiac physiology.