Introduction
Left atrial appendage closure (LAAC) is increasingly utilized to mitigate stroke risk in patients unable to tolerate anticoagulation. Serious complications from LAAC with the WATCHMAN™ device are rare. According to the NCDR registry, major in-hospital adverse events occur in only 2.16% of cases and 1.39% of these events were due to pericardial effusion requiring intervention (1). To date, there have been no reported risk factors for pericardial effusion development following LAAC. In the PINNACLE FLX trial, there were no acute pericardial effusions requiring drainage within the first 7 days from WATCHMAN FLX™ device implant; however, 3 patients required pericardiocentesis between 7 and 45 days (2). We present a case series of two patients with hyperdynamic left atrial appendages who developed pericardial effusions following WATCHMAN FLX™ implantation.