Atrial Septal Defect (ASD) By Lee B Beerman, MD, Children's Hospital of Pittsburgh of the University of Pittsburgh School of Medicine Reviewed / Revised Apr 2023 View Patient Education Pathophysiology Symptoms and Signs Diagnosis Treatment Key Points More Information Topic Resources Split Second Heart Sound... Normal circulation with represent... Atrial septal defect Overview of Atrial Septal... An atrial septal defect (ASD) is an opening in the interatrial septum, causing a left-to-right shunt and volume overload of the right atrium and right ventricle.