• Is a fibroserous sac that encloses the heart and the roots of the great vessels and occupies the middle mediastinum.
• Is composed of the fibrous pericardium and serous pericardium.
• Receives blood from the pericardiophrenic, bronchial, and esophageal arteries. Is innervated by vasomotor and sensory fibers from the phrenic and vagus nerves and the sympathetic trunks.

• Is a strong, dense, fibrous layer that blends with the adventitia of the roots of the great vessels and the central tendon of the diaphragm.

• Consists of the parietal layer , which lines the inner surface of the fibrous pericardium, and the visceral layer , which forms the outer layer (epicardium) of the heart wall and the roots of the great vessels.

• Is a potential space between the visceral layer of the serous pericardium (epicardium) and the parietal layer of the serous pericardium lining the inner surfaces of the fibrous pericardium.

Transverse sinus

• Is a subdivision of the pericardial sac , lying posterior to the ascending aorta and pulmonary trunk, anterior to the SVC, and superior to the left atrium and the pulmonary veins.
• Is of great importance to the cardiac surgeon because, while performing surgery on the aorta or pulmonary artery, a surgeon can pass a finger and make a ligature through the sinus between the arteries and veins, thus stopping the blood circulation with the ligature.

Oblique sinus

• Is a subdivision of the pericardial sac behind the heart, surrounded by the reflection of the serous pericardium around the right and left pulmonary veins and the inferior vena cava (IVC).