Sinus of pulmonary veins

The sinus of pulmonary veins is the roof of the smooth-walled part of the left atrium. The vestibule and body are also smooth-walled.

In embryological and developmental context, the term "sinus of pulmonary veins" refers to the region where the pulmonary veins converge before entering the left atrium. During cardiac development, the pulmonary veins initially form a common pulmonary vein that drains into the primitive left atrium. This common vein, sometimes referred to as the "pulmonary venous sinus," subsequently incorporates into the posterior wall of the left atrium, resulting in the four separate pulmonary vein ostia seen in the mature heart