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• The pericardium is a fibroserous membrane that covers the heart and the start of its great vessels.
• The pericardium is a closed sac made of two layers.

Fibrous Pericardium

• It's the tough, external layer that is continuous with the diaphragm's central tendon.
• The internal surface is lined with a glistening serous membrane, specifically the parietal layer of the serous pericardium.
• This layer is continuous superiorly with the tunica adventitia of the great vessels entering/leaving the heart and the pretracheal layer of deep cervical fascia.
• The fibrous pericardium attaches anteriorly to the sternum's posterior surface via sternopericardial ligaments.
• It binds posteriorly with loose connective tissue to structures in the posterior mediastinum.
• Inferiorly, it continues with the diaphragm's central tendon, and this site is known as the pericardiacophrenic ligament.

Serous Pericardium

• It is comprised mainly of mesothelium, a single layer of flattened cells forming an epithelium.
• Mesothelium lines both the fibrous pericardium's internal surface and the heart's external surface.
• The visceral layer of serous pericardium forms the epicardium (the outermost of three layers of the heart wall).
• The epicardium extends onto the start of the great vessels.
• It becomes continuous with the parietal layer of serous pericardium where the aorta and pulmonary trunk leave the heart.
• It is continuous where the SVC, inferior vena cava (IVC), and pulmonary veins enter the heart.

Heart Position

• The heart and the roots of its great vessels, along with the pericardial sac, lie posterior to the sternum.
• They are also posterior to the costal cartilages and anterior ends of the 3rd-5th ribs on the left side.
• The heart and pericardial sac are situated obliquely, with roughly two-thirds to the left and one-third to the right of the median plane.

Pericardial Cavity

• It is a potential space between the opposing parietal and visceral layers of serous pericardium.
• This cavity normally contains a thin fluid film, which enables the heart to move and beat with minimal friction.

Sinuses of the Pericardium

• There are two sinuses in the serous pericardium: transverse and oblique.
• The transverse sinus is a recess behind the pulmonary trunk and ascending aorta.
  • Anterior boundary: Pulmonary trunk and ascending aorta
  • Posterior boundary: SVC and the upper part of the two atria
  • Superior boundary: Right pulmonary artery
  • Inferior boundary: Primarily the left two atria
• The transverse pericardial sinus is important to cardiac surgeons.
  • After the pericardial sac is opened anteriorly, a finger can pass through the transverse pericardial sinus posterior to the aorta and pulmonary trunk.
• Passing a surgical clamp or placing a ligature around these vessels, inserting coronary bypass tubes, and tightening the ligature enables surgeons to stop or divert blood circulation in these arteries during cardiac surgery such as coronary artery bypasses.
• The oblique pericardial sinus is the J-shaped zone of reflection surrounding the veins.
• The cul-de-sac formed within the 'J', posterior to the left atrium, is the oblique pericardial sinus.

Arterial Supply

• The main supply comes from the pericardiacophrenic artery (a slender branch of the internal thoracic artery), which is the artery that accompanies or parallels the phrenic nerve to the diaphragm.
• Smaller contributions include:
  • Musculophrenic artery (a terminal branch of the internal thoracic artery).
  • Bronchial, esophageal, and superior phrenic arteries (branches of the thoracic aorta).
  • Coronary arteries, provide supply only to the visceral layer of serous pericardium and the first branches of the aorta.

Nerve Supply

• The pericardium is supplied by the phrenic nerves (C3-C5), the primary source of sensory fibers.
• The vagus nerves have an uncertain function in the pericardium.
• Sympathetic trunks control vasomotor functions.

Clinical significance

• Pericardial effusion is an abnormal accumulation of fluid within the pericardial cavity.
• Cardiac tamponade is a buildup of blood or fluid in the pericardial sac, putting pressure on the heart and possibly preventing it from effectively pumping.