What Makes The Lub Sound ((better)) Jun 2026

The "dub" is the . It occurs at the beginning of ventricular diastole (relaxation). It is caused by the closure of the Semilunar Valves (the Aortic and Pulmonary valves). When the ventricles relax, the blood in the arteries attempts to flow back into the heart, snapping these valves shut. This creates a shorter, higher-pitched sound than S1.

The "lub" itself comes from the vibrations of the blood and heart structures as these valves block flow from moving backward into the upper chambers (atria). Key Facts About the "Lub" what makes the lub sound