There are two pericardial sinuses: transverse and oblique.
- The sinus, enclosed between the limbs of the inverted U of the venous mesocardium lies behind the left atrium and in between left and right pulmonary veins. This is known as the oblique sinus.
- The passage between the venous and arterial mesocardia—i.e., behind the aorta and pulmonary artery and anterior to the superior vena cava —is termed the transverse sinus. Also, the sinus that forms in the pericardial cavity where the dorso-mesentary pericardium reside. Note: This sinus is clinically important because passing one end of clamp through the sinus, and the other end anterior to the aorta/pulmonary trunk will allow complete blockage of blood output. This is done during some heart surgeries.