A two-layered sac surrounding the heart is pericardium/perichondrium.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks about the two-layered sac that surrounds the heart, specifically whether it is called the pericardium or perichondrium.

2. **Identifying the Correct Term**: The correct term for the two-layered sac surrounding the heart is "pericardium." The term "perichondrium" refers to a layer of connective tissue that surrounds cartilage, which is not related to the heart.

3. **Describing the Pericardium**: The pericardium is often referred to as the pericardial sac. It consists of two layers:
- **Outer Layer**: This is known as the Fibrous Pericardium, which is made of strong connective tissue. Its primary role is to provide structural support and protection to the heart.
...