What is heart rate ?

Explanation

### Step-by-Step Solution:

1. **Definition of Heart Rate**: Heart rate is defined as the number of times the heart beats in a specific period, usually measured in beats per minute (bpm).

2. **Function of the Heart**: The heart is a major organ of the circulatory system, responsible for pumping blood throughout the body. It works in coordination with the lungs to ensure that organs receive oxygenated blood and return deoxygenated blood back to the heart.

3. **Structure of the Heart**: The human heart has four chambers: two atria and two ventricles. The atria receive blood, and when they contract, they send blood into the ventricles.

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