👉 In medicine, a pericardial sac or sac of the pericardium is a fluid-filled sac that surrounds the heart. It is located in the left side of the chest and is composed of two layers: the pericardium (a layer of thin, elastic tissue) and the pericardial sac (a layer of fluid). The pericardial sac is surrounded by the muscle layer called the periosteum, which is made up of connective tissue.
