​The characteristic features and causes of different heart sounds during a cardiac cycle of humans are given in the following statements:

A. The second heart sound is loud and sharp when the diastolic pressure is decreased in the aorta or pulmonary artery.
B. Sudden closure of atrioventricular (AV) valves at the start of ventricular systole causes vibration that produces the first heart sound.
C. The second heart sound is caused by the vibration associated with the closure of aortic and pulmonary valves after the end of ventricular systole.
D. The first heart sound is soft when heart rate is low, as the ventricles are well filled with blood and the leaflets of AV valves float together before systole.

Which one of the following options represents the combination of all correct statements?

Correct option is C

​A. The second heart sound is loud and sharp when the diastolic pressure is decreased in the aorta or pulmonary artery. (Incorrect)

• The second heart sound (S₂) occurs due to closure of the aortic and pulmonary valves.
• A decrease in diastolic pressure actually reduces the intensity of the second heart sound, rather than making it loud and sharp.

B. Sudden closure of atrioventricular (AV) valves at the start of ventricular systole causes vibration that produces the first heart sound. (Correct)

• The first heart sound (S₁) is generated when the mitral and tricuspid valves close at the beginning of ventricular systole.
• This closure causes vibrations in surrounding structures, producing the characteristic "lub" sound.

C. The second heart sound is caused by the vibration associated with the closure of aortic and pulmonary valves after the end of ventricular systole. (Correct)

• The second heart sound (S₂) is generated when the aortic and pulmonary valves close at the end of ventricular systole, leading to the "dub" sound.

D. The first heart sound is soft when heart rate is low, as the ventricles are well filled with blood and the leaflets of AV valves float together before systole. (Correct)

• When heart rate is low, ventricles fill more completely, causing the AV valves to close more passively with less force, resulting in a softer first heart sound.

Information Booster:

1. Heart sounds are produced due to the closure of heart valves and the vibrations they generate.
2. First heart sound (S₁) ("lub") occurs due to closure of mitral and tricuspid valves at the start of ventricular systole.
3. Second heart sound (S₂) ("dub") occurs due to closure of aortic and pulmonary valves at the end of ventricular systole.
4. The loudness of S₁ and S₂ varies based on heart rate, blood volume, and pressure changes.
5. S₂ can be split into two sounds (A₂ and P₂) due to the slightly delayed closure of the pulmonary valve.
6. Abnormal heart sounds (murmurs) indicate valvular defects or turbulent blood flow.