Inclusion Criteria:  Patients ≥ 18 years Present, written informed consent from the patient paroxysmal, persistent, or permanent atrial fibrillation not longer than 10 years according to guidelines (ACC, AHA, ESC) planned cardiac surgery on the mitral valve ECHO parameters : LA size a.p. ≤ 55mm  Exclusion Criteria:  permanent atrial fibrillation longer than 10 years ECHO parameters : LA size a.p. > 55mm pregnancy life expectancy < 12 months lack of cognitive or mental capacity to participate in the study Patients who are to be included in another clinical (interventional) study at the same time or who are already participating in such a study