Three dimensional transesophageal echocardiography (3DTEE) is superior to two dimensional transesophageal echocardiography (2DTEE) as it provides all atrial septal information from a single view. To evaluate 3DTEE role in analysis of atrial septal aneurysm (ASA) and in device closure guiding. Three dimensional transesophageal echocardiography were recorded with Vivid*E9,GE system over 14months. ASAs were classified into 4 types (A: with PFO, B: with one ASD, C: with 2 ASDs, and D: with multiple fenestrations). Each aneurysm was assessed according to its type, shape, dimensions, orientation, aneurysmal tissue, and the surrounding rims. All patients passed to transcatheter aneurysm closure. A total of 26 patients with ASAs were assessed (7 imperforated aneurysms excluded). The remaining 19 patients' age was 12.84±5.82years. Four patients had type A aneurysms, 6 had type B, 4 had type C, and 5 had type D. 3DTEE demonstrated oval aneurysms in 17 patients. The orientation was oblique in 8 patients, vertical in 7, and horizontal in 4. The ASAs dimensions were 23.5±5.1, 23.2±5.1, and 22.0±4.0mm for oblique, vertical, and horizontal axes. Percutaneous closure succeeded in 18 patients. Balloon sizing was used in 4 patients. Devices used were: In type A:PFO devices, in type B:ASO devices, in type C:two patients required two ASO devices in each patient and two patients required one cribriform device, and in type D:Cribriform devices used for three patients, PFO for one and ASO for one. LA, LUPV, and RUPV approaches were used. Aspirin was received for 6months. Three dimensional transesophageal echocardiography helps to select aneurysms suitable for transcatheter closure, select the suitable devices, and guide the transcatheter procedure.