What is the name of the double membrane sac that encloses the heart?

The name of the double membrane sac that encloses the heart is known as the pericardium. This structure consists of two layers: the visceral pericardium, which is the inner layer that directly covers the heart, and the parietal pericardium, which forms the outer layer. The space between these two layers is filled with pericardial fluid, which serves to lubricate and reduce friction as the heart beats.

The pericardium plays an important role in protecting the heart and providing a stabilizing effect, preventing the heart from over-expanding and allowing for the proper functioning of the cardiac muscle during the heart's pumping action. Understanding the anatomy and function of the pericardium is essential for comprehending how the heart operates within the cardiovascular system. The other options refer to different anatomical structures related to respiratory and cardiac systems, but they do not encompass the specific protective and enclosing function of the pericardium.