Which of the following statements about heart sound is correct?

Options

A. Lub is diastolic heart sound.
B. Lub occurs due to opening of semilunar valves
C. Dub can't be easily heard with a stethoscope.
D. Dub occurs due to closure of semilunar valves.

Answer

To determine which statement about heart sounds is correct, we can analyze the options related to the two primary heart sounds: "lubb" (or "lub") and "dub."

### Step-by-Step Solution:

1. **Understanding Heart Sounds**:
- The heart produces two main sounds during the cardiac cycle: "lubb" (S1) and "dub" (S2).
- The "lubb" sound occurs when the atrioventricular (AV) valves close, marking the beginning of ventricular contraction (systole).
- The "dub" sound occurs when the semilunar valves close, marking the end of ventricular contraction and the beginning of ventricular relaxation (diastole).

2. **Analyzing the Options**:
- **Option 1**: "Lubb is a diastolic heart sound."
- This is incorrect because "lubb" occurs during systole when the AV valves close.
- **Option 2**: "Lubb occurs due to the opening of the semilunar valve."
- This is also incorrect because no sound is produced during the opening of the valves; sounds are produced during closure.
- **Option 3**: "A dub can't be easily heard with a stethoscope."
- This statement is misleading. While some heart sounds may be faint, the "dub" sound is typically audible with a stethoscope.
- **Option 4**: "A dub occurs due to the closure of the semilunar valve."
- This statement is correct as "dub" is indeed the sound produced when the semilunar valves close after blood is ejected from the ventricles.

3. **Conclusion**:
- The correct statement about heart sounds is that "a dub occurs due to the closure of the semilunar valve."

### Final Answer:
The correct statement about heart sounds is: "A dub occurs due to the closure of the semilunar valve."