In human the closed sac which surrounds the heart is:

Explanation

Yes, the closed sac which surrounds the heart in humans is the pericardium. The pericardium is a double-walled sac that surrounds the heart and the roots of the major blood vessels that extend from the heart. The pericardium is made up of two layers: the fibrous pericardium and the serous pericardium.The fibrous pericardium is the outermost layer of the pericardium. It is a tough, fibrous sac that protects the heart and helps to keep it in place.The serous pericardium is the innermost layer of the pericardium. It is a thin, delicate sac that is made up of two layers: the parietal pericardium and the visceral pericardium.The parietal pericardium is attached to the fibrous pericardium. Whereas, the visceral pericardium is attached to the surface of the heart. The space between the parietal pericardium and the visceral pericardium is called the pericardial cavity. The pericardial cavity contains a small amount of fluid that helps to lubricate the heart and allow it to move freely.