An atrial septal defect is a congenital heart defect where the wall between the right and left atria does not close properly, leaving a hole between the two atria.
Review Date 7/7/2020
Updated by: Thomas S. Metkus, MD, Assistant Professor of Medicine and Surgery, Johns Hopkins University School of Medicine, Baltimore, MD. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.