To evaluate the efficacy of Cogmed Working Memory Training compared with the standard of care to improve executive function and social outcomes in adolescents with congenital heart disease (CHD) who underwent open-heart surgery in infancy and to identify factors associated with changes in outcomes following the intervention. In a single-center, randomized controlled trial, adolescents (13-16 years) with CHD were randomly assigned to either Cogmed (home-based 45-minutes sessions for 5-8 weeks) or to a control group. The primary outcome was working memory. Secondary outcomes included inhibitory control and cognitive flexibility as well as parent-reported executive function, symptoms of attention deficit hyperactivity disorder, and social outcomes. All measures were assessed at baseline, post-treatment (1-3 weeks post-training) and at 3-month follow-up. Data were analyzed using an intention-to-treat approach. Sixty adolescents with CHD participated (28 assigned to Cogmed). No improvement at the post-treatment or 3-month follow-up assessments was found for the primary outcome measure of working memory. Compared with the control group, participants assigned to the intervention demonstrated benefits in inhibitory control and attention at the 3-month follow-up (P = .02) and in parent-reported cognitive regulatory skills at post-treatment and 3-month follow-up (P = .02 and P = .04, respectively). Preterm birth, biventricular CHD, and history of attention deficit hyperactivity disorder diagnosis were associated with improved response to the intervention. Cogmed intervention produced improvements in the self-regulatory control abilities of adolescents with CHD. The training did not enhance other areas of executive function or behavioral outcomes. Further studies are needed to evaluate the longer-term potential benefits to other domains. Clinicaltrials.gov: NCT02759263. Copyright © 2020 Elsevier Inc. All rights reserved.