overriding aortic valve DA Fyler:1432 MP:0000273 MPheno.ontology aortic dextroposition congenitally abnormal position of the aorta where the valve origin straddles the ventral septum and so receives ejected blood from the right ventricle as well as the left, frequently in conjunction with a ventricular septal defect dextroposition of the aorta overriding aorta abnormal heart and great artery attachment