What is the fibrous outer fluid filled layer that covers the heart?

The fibrous outer fluid-filled layer that covers the heart is known as the pericardium. This structure serves several important functions. It provides a protective barrier around the heart, shielding it from infections and physical trauma. Additionally, the pericardium contains a small amount of fluid that creates a lubricated environment, allowing the heart to move smoothly within the chest cavity as it beats. This function is essential for preventing friction between the heart and surrounding structures.

The other layers mentioned in the options are important components of heart anatomy but serve different roles. The endocardium lines the inside of the heart chambers, ensuring a smooth surface for blood flow. The epicardium is the outermost layer of the heart wall, but it is different from the pericardium as it is the innermost layer of the pericardial sac. The myocardium is the thick muscle layer responsible for the heart's contractions. Understanding these differences helps clarify the specific role of the pericardium as the protective and fluid-filled outer layer surrounding the heart.