What prevents backflow of blood inside the heart during contraction ?

Options

A. Valves in heart
B. Thick muscular walls of ventricles
C. Thin walls of atria
D. All of these

Explanation

**Step-by-Step Solution:**

1. **Understanding the Heart Structure**: The human heart consists of four chambers: two atria (upper chambers) and two ventricles (lower chambers). These chambers are separated by walls known as valves.

2. **Role of Valves**: The primary function of these valves is to ensure that blood flows in one direction through the heart. During the contraction of the heart (systole), these valves close to prevent any backflow of blood.

3. **Identifying the Correct Answer**: Among the options provided, the correct one states that the valves in the heart prevent the backflow of blood. This is the main function of the valves during heart contraction.

4. **Eliminating Incorrect Options**: Other options mention the thick muscular walls of the ventricles and atria. While these walls are important for the pumping action of the heart, they do not specifically prevent backflow. Therefore, these options can be eliminated.

5. **Conclusion**: The correct answer to the question is that the valves in the heart prevent the backflow of blood during contraction.

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