abnormal aortic sac morphology dilated aortic sac 2014-01-01T13:22:33Z MP:0012511 MPheno.ontology abnormally stretched or widened aperture of the luminal space of the endothelial lined dilation that is located at the arterial pole of the heart just above (distal to) the truncus arteriosus in mammalian embryos; it is the primordial vascular channel from which the aortic arches (and eventually the dorsal aortae) arise; the aortic sac is homologous to the ventral aorta of gill-bearing vertebrates csmith