This pictorial assay illustrates the methodology of evaluating the atrial septal defects by three dimensional transesophageal echocardiography with the help of representative images. The article starts by discussing the technical details of how to acquire and crop the dataset to reconstruct the transesophageal three dimensional echocardiographic images of the inter atrial septum. Next, the anatomical details of the normal inter atrial septum are illustrated, followed by representative examples of all the possible defects of inter atrial septum. All the images have been reproduced in a uniform pattern which is similar to the view of the inter atrial septum that is seen in the real life situation by the surgeon.