Inflammation of the pericardium is called pericarditis. Another type, mesothelium, forms the walls of the pericardium, pleurae, and peritoneum. A double-membraned sac called the pericardium surrounds the heart and attaches to the mediastinum. The inferior sternopericardial ligament attaches the pericardium to the posterior xiphoid process. Pericarditis is inflammation of the pericardium (the fibrous sac surrounding the heart). The tough outer surface of the pericardium is called the fibrous membrane. The fibrous pericardium is the most superficial layer of the pericardium. The septum is then repaired, using material from the pericardium. A thin-walled sac, known as the pericardium, completely surrounds the heart. These are surrounded by a double-membraned sac called the pericardium. The pericardium is the sack that surrounds the heart. Sometimes the pericardium (Xin Bao) is included. It is the most common condition affecting the pericardium. The Yin meridians of the arm are Lung, Heart, and Pericardium.