Left ventricle is the thickest chamber of the heart.

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). The ventricles are responsible for pumping blood out of the heart.

2. **Identifying the Chambers**: The right ventricle and left ventricle are the two lower chambers. The right ventricle pumps deoxygenated blood to the lungs for oxygenation, while the left ventricle pumps oxygenated blood to the rest of the body.

3. **Function of the Left Ventricle**: The left ventricle is crucial because it pumps oxygen-rich blood into the aorta, which then distributes it throughout the body. This requires the left ventricle to generate a significant amount of pressure.

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