Final answer:
The membrane covering the outer surface of the heart is called a serous membrane. It is a part of the pericardium, which protects the heart. The serous membrane produces serous fluid to reduce friction as the heart contracts.
Step-by-step explanation:
The membrane covering the outer surface of the heart is a serous membrane.
Serous membranes are thin membranes that cover the walls and organs in the body cavities.
In the case of the heart, the serous membrane is called the pericardium, which covers and protects the heart.
The serous membrane secretes a lubricating fluid called serous fluid that reduces friction as the heart contracts.