The pericardial sinuses are impressions in the pericardial sac formed between the points where great vessels enter it.There are three pericardial sinuses: superior, transverse and oblique.

[1] During pericardial effusion, fluid may build up in the pericardial sinuses.

[3] This may be diagnosed with transoesophageal echocardiography.

[3] This article incorporates text in the public domain from page 526 of the 20th edition of Gray's Anatomy (1918)