An 86-year-old lady with severe aortic stenosis and interventricular membranous septal aneurysm underwent transfemoral transcatheter aortic valve implantation (TAVI). A balloon-expandable valve was deployed after a difficult native valve crossing. Transesophageal echocardiography showed a rapidly accumulating pericardial effusion, with pericardial thrombus and subsequent cardiac tamponade. The angiographic views raised suspicion of aortic root perforation. Median sternotomy was performed because of sudden hemodynamic collapse.The report presents the uncommon association between severe aortic stenosis and interventricular membranous septal aneurysm in an octogenarian and discusses its impact on the development of a post-TAVI major complication.