Different surgical techniques for complete atrioventricular septal defect (CAVSD) repair have been described, with the double-patch technique being most frequently employed. More recently a newer technique using a modified single-patch repair has been advocated. We hypothesized that the modified single-patch technique would result in an increased incidence of the two major post-repair comorbidities, namely, distortion of the left AV valve (LAVV) leaflets and narrowing of the left-ventricular outflow tract (LVOT). We studied 14 patients with CAVSD who underwent either traditional double-patch technique [group 1 (n = 7)] or modified single-patch technique [group 2 (n = 7)]. Preoperative and immediate postoperative two-dimensional (2D) echocardiograms, as well as follow-up 2D and three-dimensional (3D) studies, were reviewed. For group 1, the median age at repair was 4.1 months with a median duration from surgical repair and last echocardiogram of 44 months. For group 2, the median age at repair was 3 months with a median duration from surgical repair and last echocardiogram of 28 months. The two groups had similar demographics and ventricular septal defect size before surgery. For the LAVV, no significant difference was observed with respect to LAVV annulus size, tenting height, and the size of the vena contracta. Furthermore, there was no significant difference in the 2D echocardiographic areas and volumes of the LVOT between pre-repair and immediate post-repair studies for both groups. At the last evaluation, although there had been growth of the LVOT in both groups, no significant difference between areas and volumes were observed. Areas of the LVOT measured by 3D echocardiography on the final study showed no significant statistical difference between both groups. There was good correlation of the areas measured by 2D and 3D echocardiography within each group. In this small group, modified single-patch technique does not appear to tether the LAVV or promote an increase in regurgitation. In the short term, LVOT growth is unaffected, and the repair does not promote LVOT obstruction. 3D echocardiography is useful for area measurements of the LVOT and showed good correlation with areas measured by assumption of the LVOT shape as determined using 2D techniques.