Which hormone is secreted by the heart ? Give its role.

Explanation

**Step-by-Step Solution:**

1. **Identify the Hormone Secreted by the Heart:**
The heart secretes a hormone known as Atrial Natriuretic Factor (ANF).

2. **Understand the Nature of ANF:**
ANF is a polypeptide hormone composed of 28 amino acids, which classifies it as a protein hormone.

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