• The cul-de-sac enclosed between the limbs of the inverted U of the venous mesocardium lies behind the left atrium
  Left atrium
  The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...
  
   and is known as the oblique sinus. .

• The passage between the venous and arterial mesocardia—i.e., between the aorta
  Aorta
  The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
  
   and pulmonary artery
  Pulmonary artery
  The pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries that carry deoxygenated blood....
  
  in front and the superior vena cava behind—is termed the transverse sinus. Also, the sinus that forms in the pericardial cavity where the dorso-mesentary pericardium reside.
• Can be used to pass ligature during cardiac surgery.

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