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?