What Makes The Lub Sound In The Heart

Shortly after the "lub," you hear a shorter, higher-pitched "dub." This sound is caused by the semilunar valves (the aortic and pulmonary valves) snapping shut.

| Feature | | Dub (S2) | |---------|--------------|--------------| | Which valves? | Mitral & Tricuspid (AV valves) | Aortic & Pulmonary (semilunar valves) | | When? | Start of ventricular contraction | End of ventricular contraction | | Cardiac phase | Systole begins | Diastole begins | what makes the lub sound in the heart