[TA] a passage in the pericardial sac between the origins of the great vessels, i.e., posterior to the intrapericardial portions of the pulmonary trunk and ascending aorta and anterior to the superior vena cava and superior to the atria; it is formed as a result of the flexure of the heart tube, partially approximating the great venous and arterial vessels. SYN: sinus transversus pericardii [TA], Theile canal, transverse sinus of pericardium.