The first heart sound is

Options

A. "Lub"sound at the end of systole
B. "Dub"sound at the end of systole
C. "Lub" sound at the end of systole
D. "Dub"sound at the beginning of systole

Answer

**Step-by-Step Solution:**

1. **Understanding Heart Sounds**: The heart produces sounds during its functioning, which are primarily due to the closing of heart valves and the movement of blood through the heart chambers.

2. **Types of Heart Sounds**: There are four main types of sounds generated by the heart:
- The first sound (S1) occurs at the beginning of systole.
- The second sound (S2) occurs at the end of systole.
- Additional sounds may arise from vibrations of the ventricular walls and atrial contractions, but these are less significant and not always audible.

3. **Identifying the First Heart Sound**: The first heart sound, known as "lub," is produced when the atrioventricular (AV) valves close at the beginning of systole. This is the sound that signifies the start of the heart's contraction phase.

4. **Analyzing the Options**: The question provides four options regarding the first heart sound:
- Option A: "lub sound at the end of systole" - Incorrect, as the first sound occurs at the beginning of systole.
- Option B: "dub sound at the end of systole" - Incorrect, as this refers to the second heart sound.
- Option C: "lub sound at the beginning of systole" - Correct, as this accurately describes the first heart sound.
- Option D: "dub sound at the beginning of systole" - Incorrect, as this refers to the second heart sound.

5. **Conclusion**: The correct answer is Option C: "lub sound at the beginning of systole."

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