Which heart sound occurs when the ventricles are relaxing and the semilunar valves close?

Which heart sound occurs when the ventricles are relaxing and the semilunar valves close?

• A. Lubb
• B. Dubb
• C. Lubb-Dubb
• D. Sigh

Answer: (C)

During the cardiac cycle, each heart sound marks a valve event. The second sound, produced when the ventricles are relaxing, comes from the semilunar valves closing as the pressure in the ventricles drops below that in the aorta and pulmonary artery. This creates the short, higher-pitched “dub.” So the sound heard at ventricular relaxation when the semilunar valves close is the “dub.” The sequence of both sounds is often heard as “lub-dub,” while the single closing of the semilunar valves is just the “dub.”

During the cardiac cycle, each heart sound marks a valve event. The second sound, produced when the ventricles are relaxing, comes from the semilunar valves closing as the pressure in the ventricles drops below that in the aorta and pulmonary artery. This creates the short, higher-pitched “dub.” So the sound heard at ventricular relaxation when the semilunar valves close is the “dub.” The sequence of both sounds is often heard as “lub-dub,” while the single closing of the semilunar valves is just the “dub.”