heart septal defect heart septal defect heart septal defect refers to a congenital heart defect of one of the septa of the heart. atrial septal defect atrioventricular septal defect ventricular septal defect heart septal defectspecialtycardiology although aortopulmonary septal defects are defects of the aorticopulmonary septum, which is not technically part of the heart, they are sometimes grouped with the heart septal defects.