Coarctation of the aorta. Coarctation of the aorta is a common cardiovascular disorder with an unknown etiology. In the preductal type, blood flows from a patent ductus into the distal aorta. When the coarctation is juxtaductal or postductal, blood flows to the lower extremities by way of the subclavian arteries and collaterals. Plain films may show the reverse sign in postductal coarctation. Arteriography is the gold standard for making the diagnosis. However, magnetic resonance imaging will probably become an increasingly important diagnostic tool. The treatment of choice is surgery, with complete resection of the stenosed segment. 