New-onset cardiac mass due to left atrial appendage inversion during cardiac surgery.

Cardiac mass assessment is challenging in the intraoperative scenario. We present the case of a 22-year-old woman with a new-onset left atrial mass during cardiopulmonary bypass following closure of a ventricular septal defect. We discuss the role of intraoperative echocardiographic examination, the differential diagnosis, and raise awareness of the left atrial appendage as a rare etiology of an acute left atrial mass.