orthotopic		Located in an anatomically normal recipient site, often in reference to transplantation of an organ.
ostium primum ASD		see atrial septal defect.
outlet VSD		see ventricular septal defect.
over-and-under ventricles		see supero-inferior heart.
overriding valve		An A-V valve that empties into both ventricles or a semilunar valve that originates from both ventricles.
overriding valve		An A-V valve that empties into both ventricles or a semilunar valve that originates from both ventricles.