What heart sound is created during isovolumic relaxation?

What heart sound is created during isovolumic relaxation?

• A. The second heart sound, Dubb (S2), created by closing of the SL valves.
• B. The first heart sound, Lubb (S1), created by closing of the AV valves.
• C. A third heart sound (S3).
• D. The fourth heart sound (S4).

Answer: (A)

During isovolumic relaxation the ventricles start to relax but all valves are still closed, so there’s no blood flow change until the AV valves reopen. The sound that marks this transition is the second heart sound, produced by the abrupt closure of the semilunar valves (aortic and pulmonary). This closing ends systole and begins diastole, so S2 is heard as the Dubb. The other sounds occur at different times: S1 happens with AV valve closure at the start of systole, S3 is a rapid filling sound in early diastole, and S4 is an atrial contraction sound late in diastole.

During isovolumic relaxation the ventricles start to relax but all valves are still closed, so there’s no blood flow change until the AV valves reopen. The sound that marks this transition is the second heart sound, produced by the abrupt closure of the semilunar valves (aortic and pulmonary). This closing ends systole and begins diastole, so S2 is heard as the Dubb. The other sounds occur at different times: S1 happens with AV valve closure at the start of systole, S3 is a rapid filling sound in early diastole, and S4 is an atrial contraction sound late in diastole.