The first heart sound has two components due to split closure of the mitral and tricuspid valves, but these components are generally not audible. This describes which heart sound?

The first heart sound has two components due to split closure of the mitral and tricuspid valves, but these components are generally not audible. This describes which heart sound?

• A. S1
• B. S2
• C. S3
• D. S4

Answer: (A)

The first heart sound is heard at the start of ventricular systole and is produced by the closure of the atrioventricular valves (mitral and tricuspid). The two components come from the slightly different timing of these closures on the left and right sides of the heart. In many people those closures are so close in time that they blend into a single sound, so you don’t hear a distinct split. That matches the description given. The second heart sound, by contrast, comes from the semilunar valves and can show a noticeable split with inspiration; S3 and S4 are additional sounds not tied to AV valve closure at the onset of systole.

The first heart sound is heard at the start of ventricular systole and is produced by the closure of the atrioventricular valves (mitral and tricuspid). The two components come from the slightly different timing of these closures on the left and right sides of the heart. In many people those closures are so close in time that they blend into a single sound, so you don’t hear a distinct split. That matches the description given. The second heart sound, by contrast, comes from the semilunar valves and can show a noticeable split with inspiration; S3 and S4 are additional sounds not tied to AV valve closure at the onset of systole.