Give appropriate biological or technical terms for the following:
The relaxation phase of the heart.

Explanation

**Step-by-Step Solution:**

1. **Understanding Heart Phases**: The heart has two main phases during its cycle: contraction and relaxation. The contraction phase is known as systole, while the relaxation phase is known as diastole.

2. **Identifying the Relaxation Phase**: The question specifically asks for the relaxation phase of the heart. This phase is when the heart muscle relaxes after contracting, allowing the chambers of the heart to fill with blood.

3. **Defining Diastole**: The relaxation phase of the heart is referred to as "diastole." During diastole, the heart chambers (atria and ventricles) are relaxed, and blood flows into them.

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