Our patient presented with known mechanical mitral valve endocarditis documented by 2D transesophageal echocardiogram (TOE) from a recent hospitalization at an outside facility. On admission to our center, there was no prior knowledge of an incompletely ligated left atrial appendage including by patient- or family-reported history, review of outside records, or the outside 2D TOE report. A 3D TOE performed at our center to assess her pathology, since a month had passed from her prior hospitalization, revealed a left atrial appendage (LAA) ligation with evidence of communication to the left atrium and with clot present in the appendage. This case report highlights the common finding of incomplete closure of the LAA following surgical ligation thus making it inadequate for stroke prevention in patients with atrial fibrillation, and that 3D TOE plays a valuable role in assessing the durability of LAA ligation.