The pericardium is a double-walled sac that surrounds the heart, providing protection and support. It consists of two layers: the outer fibrous layer and the inner serous layer, which is further divided into the parietal and visceral layers. This structure helps to anchor the heart in place and prevents excessive movement within the chest cavity. The pericardial cavity, located between the two serous layers, contains a small amount of fluid that reduces friction as the heart beats. This fluid allows the heart to move smoothly during contractions, contributing to efficient blood circulation throughout the body.