Left atrial dissection is an uncommon entity, and is generally associated with mitral valve surgery, blunt chest trauma, intramyocardial dissecting hematoma after AMI, Behçet's disease, and infective endocarditis. Moreover, debridement of very calcified valves or inadvertent incision of the annulus may occur during the surgical procedure, and hemodynamic influence of a paraprosthetic leak may extend the dissection into the left atrial wall. We report a case with a mobile intimal flap of the left atrial wall detected by intraoperative transesophageal echocardiography after aortic valve replacement. An intraoperative transesophageal echocardiographic examination is needed for aortic valve replacement, especially when aortic stenosis is combined with severe annulus calcification.