The pericardium is a double-walled sac that contains the heart and the roots of the great vessels. Morphologically, it is a conical-shaped, double-walled fibro-serous membrane. It rests posteriorly to the sternum at the level of second to sixth costal cartilages and T5-T8 vertebrae.

• The pericardium is made up of two layers:
  • Fibrous pericardium
    • Hard protective external layer
    • Attached to sternum anteriorly by sterno-pericardial ligaments and fused with the central tendon of the diaphragm and great vessels to allow mobility of the pericardial sac against sudden cardiac overfilling
  • Serous pericardium
    • Smooth internal layer made up of 2 components:
      • Parietal: reflects onto fibrous pericardium
      • Visceral: reflects onto heart and great vessels and forms the epicardium, the external layer of the heart wall
• Pericardial cavity: Potential space between parietal and visceral layers. It contains a serous fluid film that occupies the cavity and functions as lubricant against friction by all chest movements.^[1][2][3]

• There are two small chambers or sinuses located where the visceral and parietal pericardia are continuous with one another within the pericardial cavity.
• Transverse sinus:
  • Located posterior to the pulmonary trunk and ascending aorta at the level between the superior vena cava and aortic arch
  • Formed after dorsal mesocardium rupture embryonically
  • Functional role is to allow the unhindered expansion of great arteries posteriorly during cardiac systole
  • Utilized surgically to pass surgical clamps or place ligatures around great arteries.
• Oblique sinus:
  • A blind recess (cul-de-sac) posterior to the left atrium between superior vena cava, right and left pulmonary veins inferior to the transverse sinus
  • Formed embryonically by the incorporation of the pulmonary vein tributaries into the left atrium
  • Functional role believed to be the expansion of the left atrium upon normal collapse of the thorax^[4][5][6]

• Pericarditis is an inflammatory condition of the pericardium.
• Pericardial effusion is fluid accumulation in the pericardial sac.
• Constrictive pericarditis occurs when there is a scar encasing, the heart that chronically constricts the filling of the heart.
• Cardiac tamponade is a medical emergency in which fluid in the pericardial sac acutely restricts the filling of the heart. This requires surgical drainage or pericardiocentesis.

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  The phrenic nerve and its relations with the vagus nerve.
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  Thoracic portion of the sympathetic trunk.
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  Liver with the septum transversum. Human embryo 3 mm long.
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  The thymus of a full-time fetus, exposed in situ.

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