Academy of Medical Sciences of Islamic Republic of Iran Archives of Iranian Medicine 1029-2977 13 4 2010 7 1 An Incidental Aneurysm of the Interventricular Membranous Septum EN Senol Yavuz Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Cuneyt Eris Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Tugrul Goncu Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Mustafa Sezen Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Yusuf Ata Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Tamer Turk Department of Cardiovascular Surgery, Bursa Yüksek Ihtisas Education and Research Hospital, Bursa, Turkey. Aneurysm of the interventricular membranous septum is a very rare cardiac anomaly in the absence of ventricular septal defect. We report the case of a 22-year-old man with aneurysm of the interventricular membranous septum incidentally determined during aortic valve surgery. The patient underwent successful aortic valve replacement and aneurysm repair. Patients with the aneurysm of the interventricular membranous septum who are asymptomatic must be followed closely in terms of potential cardiac complications.