Which statement correctly defines the 'Dub' sound?

Which statement correctly defines the 'Dub' sound?

• A. S1 is the closing of AV valves
• B. S2 is the closing of aortic/pulmonic valves
• C. S2 is the closing of AV valves
• D. S1 is the closing of semilunar valves

Answer: (B)

The Dub sound comes from the semilunar valves closing at the end of ventricular systole. When the ventricles finish ejecting blood, pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, causing the aortic and pulmonary valves to snap shut. This closure produces the second heart sound, often heard as a distinct “dub.” Sometimes the aortic valve closes a fraction of a second before the pulmonary valve, which can cause a brief splitting of S2 on inspiration. In contrast, the first heart sound, the “lub,” is due to the closure of the atrioventricular valves (mitral and tricuspid) at the start of systole, not the semilunar valves.

The Dub sound comes from the semilunar valves closing at the end of ventricular systole. When the ventricles finish ejecting blood, pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, causing the aortic and pulmonary valves to snap shut. This closure produces the second heart sound, often heard as a distinct “dub.” Sometimes the aortic valve closes a fraction of a second before the pulmonary valve, which can cause a brief splitting of S2 on inspiration. In contrast, the first heart sound, the “lub,” is due to the closure of the atrioventricular valves (mitral and tricuspid) at the start of systole, not the semilunar valves.