Twenty-six infants are described who underwent corrective surgery for coarctation of the aorta during the first year of life. Cardiac catheterization and angiography was performed in these patients pre- and postoperatively. Comparison of the angiograms shows that hypoplasia of the aortic arch did not contribute statistically to any postoperative pressure gradient. Growth of the arch, however, was less in patients with a gradient greater than 30 mm Hg. It remains unclear whether insufficient local tissue growth or only technical factors are responsible for the gradients observed. The operative procedure chosen seems to be of no importance since no statistical difference was seen with either of three operative techniques.