Background <p>Atrial Septal Defect (ASD) is a common congenital heart defect, often requiring precise diagnostic evaluation for optimal treatment. The presence of left atrial anomalous band, an anatomical variation, can complicate diagnosis and intervention and may be misinterpreted on 2D imaging. This case highlights the critical role of three-dimensional transesophageal echocardiography (3D-TEE) both for pre-procedural anatomical clarification and for intra-procedural guidance, in accurately characterizing ASD morphology, particularly when anomalous band are present, ensuring appropriate device selection and procedural planning.</p> Case presentation <p>A 25-year-old woman with a history of a cardiac murmur identified during pregnancy presented with occasional palpitations and mild foot swelling. Preoperative two-dimensional echocardiography suggested multiple ASDs, but 3D-TEE revealed a single defect with a mobile anomalous band, with the ASD measuring approximately 24*18&#xa0;mm in diameter and having a circular shape with smooth, well-defined edges, which altered the procedural approach. A single occluder was successfully deployed, leading to complete closure of the defect without complications.</p> Conclusions <p>This case emphasizes the superiority of 3D-TEE over conventional imaging in assessing ASD morphology, particularly in the presence of anatomical variations like anomalous band. We emphasize its value not only for accurate device selection and procedural planning but also as a critical teaching tool for operators learning procedural 3D echocardiography guidance. Accurate visualization of the ASD and surrounding structures facilitates optimal device selection and improves clinical outcomes.</p>