Surgical treatment of a hypoplastic aortic arch associated with an aortic coarctation is controversial. The controversy concerns the claimed need to surgically enlarge the diameter of the hypoplastic arch, in addition to resection and end-to-end anastomosis. The purpose of this prospective study is to determine the fate of the hypoplastic aortic arch after resection of the aortic coarctation and end-to-end anastomosis. Between July 1, 1988, and January 1, 1990, 15 consecutive infants less than 3 months of age with an aortic coarctation were evaluated echocardiographically. A Z-value was calculated, being the number of standard deviations the aortic arch differs from the expected value, derived from a control group. Eight of these 15 infants had a hypoplastic aortic arch with a mean Z-value of -7.14 +/- 1.39. The other seven infants had a "normal" aortic arch with a mean Z-value of -1.85 +/- 1.08. All 15 infants underwent simple coarctation resection and end-to-end anastomosis. Six months after operation the mean Z-value increased significantly in those with a hypoplastic arch to -1.08 +/- 0.69 (p less than 0.0001) and in those with a "normal" aortic arch to 0.106 +/- 0.99 (p = 0.004). No infant died in our series (0%; CL 0% to 12%) and a recoarctation developed once (12.5%; CL 2% to 36%). Therefore we believe that simple resection and end-to-end anastomosis is the operation of choice for aortic coarctation associated with a hypoplastic aortic arch despite the presence of a ventricular septal defect and that enlargement of the hypoplastic aortic arch is not necessary.