Which of the following events takes place in cardiac cycle after the end of first heart sound and before the onset of second heart sound?

Options

A. (1) atrial systole and ventricular systole
B. (2) atrial systole and ventricular diastole
C. (3) atrial diastole and ventricular systole
D. (4) joint diastole

Answer

To answer the question regarding the events that take place in the cardiac cycle after the end of the first heart sound and before the onset of the second heart sound, we can break down the cardiac cycle as follows:

### Step-by-Step Solution:

1. **Understanding the Cardiac Cycle**: The cardiac cycle consists of a series of events that occur during one heartbeat. It includes two main phases:
- **Systole**: The contraction phase where the heart chambers pump blood.
- **Diastole**: The relaxation phase where the heart chambers fill with blood.

2. **Identifying Heart Sounds**:
- The **first heart sound (S1)** occurs at the beginning of ventricular systole when the atrioventricular (AV) valves close as the ventricles contract.
- The **second heart sound (S2)** occurs at the beginning of ventricular diastole when the semilunar valves close as the ventricles relax.

3. **Events After S1 and Before S2**:
- After the first heart sound (S1), the atria (upper chambers) are in a state of diastole (relaxation) while the ventricles are in systole (contraction). This means that the atria are filling with blood while the ventricles are pumping blood out of the heart.

4. **Analyzing the Options**:
- **Option A**: Atrial systole and ventricular systole - This is incorrect because both chambers cannot contract simultaneously.
- **Option B**: Atrial systole and ventricular diastole - This is also incorrect as it does not occur after S1.
- **Option C**: Atrial diastole and ventricular systole - This is correct because after S1, the atria are relaxed (diastole) while the ventricles are contracting (systole).
- **Option D**: Atrial diastole and ventricular diastole - This is incorrect as both chambers cannot be in diastole at the same time during this phase.

5. **Conclusion**: The correct answer is **Option C: Atrial diastole and ventricular systole**. This indicates that after the first heart sound, the atria are in a relaxed state while the ventricles are contracting.