Final answer:
The heart is surrounded by a thin fluid-filled sac known as the pericardium, which protects the heart and reduces friction with other structures. The heart wall is made up of the endocardium, myocardium, and the epicardium, which is part of the pericardium.
Step-by-step explanation:
The heart is surrounded by a thin fluid-filled sac called the pericardium. This membranous structure is crucial for the protection and functionality of the heart, providing a space to facilitate vigorous pumping while minimizing friction with adjacent structures. The heart wall itself comprises three layers: the endocardium, which is the innermost layer lining the heart chambers; the myocardium, which is the middle and thickest layer made up of cardiac muscle cells; and the epicardium, which is the outermost layer. The pericardium, additionally, is divided into two layers: the fibrous pericardium and the serous pericardium, which includes the parietal and visceral layers (the latter also being referred to as the epicardium).
The heart is surrounded by a thin fluid-filled sac called the pericardium. The pericardium consists of two distinct sublayers: the outer fibrous pericardium and the inner serous pericardium. The fibrous pericardium is made of tough, dense connective tissue that protects the heart, while the serous pericardium consists of two layers - the parietal pericardium and the visceral pericardium also known as the epicardium - that help enclose and protect the heart.