In Williams' syndrome, supra-aortic stenosis is the rule and the pulmonary vessels are variably involved. This case is unusual in the degree of arterial hypoplasia, which affects the entire thoracic aorta and, to a lesser degree, the brachiocephalic branches. There is also extensive narrowing of the central pulmonary arteries extending well beyond those derived from the 6th aortic arch, out into the origins of a few of the segmental vessels. Did you notice that there is a common origin of the carotid arteries, and an abberant right subclavian artery (incompletely filled)?.