Cardiac membranous septal aneurysm is a rare congenital abnormality which occurs in 0.3% of patients as suspected congenital heart disease and in 19.1% as suspected ventricular septal defect. The main method for its diagnosis is biplane cineangiocardiography along with ventricular contrast injection. The patients with membranous septal aneurysm without hemodynamic abnormalities, complications, and concomitance with other congenital heart diseases require outpatient cardiologist's observation. Hemodynamic abnormalities, complications, and concurrent heart diseases are indications for surgery.