 Unilateral pulmonary edema after minimal-invasive mitral valve surgery is a rare but in some cases severe complications, sometimes causing extracorporeal life support. The investigators have observed over several years 5 cases of instantaneous postoperative severe pulmonary edema. After having studied the available literature on this particular topic the investigators have decided to prepare a retrospective analysis of over 200 minimal-invasive mitral valve surgery procedure focusing on radiological and clinical signs of unilateral pulmonary edema. 