A 15-year-old boy complains of pain in his legs when he runs more than 300 m. Physical examination shows temperature, 36.8deg C; pulse, 76/min; respirations, 22/min; and blood pressure, 165/90 mm Hg. The radial pulses are 4+, and the dorsalis pedis pulses are 1+. Arterial blood gas measurement shows a normal oxygen saturation level. Which of the following congenital cardiovascular anomalies is most likely to be present in this patient?

In children and adults, the coarctation is typically postductal, and collateral branches from the proximal aorta supply the lower extremities, leading to the large pulse differential between upper and lower extremities. Collaterals often involve intercostal arteries whose enlargement produces "rib notching" on chest radiographs. Diminished renal blood flow below the coarctation increases renin production and promotes hypertension. Aortic valve stenosis causes left-sided heart failure and no pressure differential in the extremities. A patent ductus arteriosus produces a small left-to-right shunt. Transposition results in a right-to-left shunt with cyanosis. Tricuspid valve atresia affects the right side of the heart.