Structure posterior to transverse pericardial sinus is
The transverse sinus is a horizontal gap between the aerial and venous ends of the hea tube.It is bounded anteriorly by the ascending aoa and pulmonary trunk,and posteriorly by the superior venacava and inferiorly by the left atrium on each side it opens into the general pericardial cavity. <img src=" /> REF.B D Chaurasia's human anatomy vol.1,fifth edition
Aoa
Pulmonary trunk
SVC
Left atrium
Thorax