The pericardium is a fibroserous sac which encloses the heart and the roots of the great vessels. It is situated in the middle mediastinum. It consists of an outer fibrous pericardium (developed from pleuropericardial membrane) and an inner serous pericardium divided into a parietal layer lining the fibrous pericardium and a visceral layer (epicardium) covering the heart and the root of great vessels. Pericardial cavity filled with serous fluid lies between parietal serous pericardium and visceral serous pericardium.
On the posterior surface of the heart, the reflection of serous pericardium (epicardium) around large veins form a recess called the oblique sinus. Oblique sinus is bounded anteriorly by left atrium, and posteriorly by the parietal pericardium and esophagus. Transverse sinus is a short passage that lies between the reflection of serous pericardium (epicardium) around arterial (aorta and pulmonary trunk) and venous ends of the heart tube. Transverse sinus is bounded anteriorly by ascending aorta and pulmonary trunk, posteriorly by SVC, and inferiorly by left atrium.
Nerve supply of the pericardium
The fibrous and parietal pericardia are supplied by phrenic nerve. They are sensitive to pain. Pain of pericarditis originate in parietal pericardium and travels through phrenic nerve. Epicardium (visceral pericardium) is supplied by autonomic nerves (sympathetic trunks and vagus) and is not sensitive to pain.