Final answer:
The outermost layer of the heart is called the epicardium.
Step-by-step explanation:
The outermost layer of the heart, also known as the outer surface and great vessels, is called the epicardium. It is the innermost layer of the pericardium, which is the membrane that surrounds and protects the heart. The epicardium allows enough room for vigorous pumping while reducing friction between the heart and other structures.