OBJECTIVE: Data supporting the use of hands-on simulation in congenital heart surgery are promising but primarily qualitative. This study aimed to demonstrate if there was an objective improvement in time and technical performance of the arterial switch procedure on 3-dimensional printed heart models by surgeons using a validated assessment method. METHODS: A total of 30 surgeons of varying experience performed the arterial switch procedure twice on 3-dimensional printed models with transposition of the great arteries during the Hands-on Surgical Training courses. Surgeons' performances were recorded and retrospectively assessed for both time and performance using the Hands-on Surgical Training-Congenital Heart Surgery tool, a validated procedure-specific assessment tool for the arterial switch. RESULTS: A total of 60 videos were scored. Eighty percent of surgeons (24/30) had improved from their first attempt. The mean total score of the first attempt performance compared with the second was 103 and 120, respectively, with a mean difference in score of 17 (95% confidence interval, 10-24). All surgeons were statistically significantly quicker in their second attempt. The mean time for the first attempt compared with the second was 1 hour, 28 minutes, 4 seconds and 1 hour, 5 minutes, and 45 seconds, respectively, with a mean difference of 0 hours, 22 minutes, 19 seconds (95% confidence interval, 0 hours, 15 minutes, 22 seconds to 0 hours, 25 minutes, 34 seconds). CONCLUSIONS: This is the first study to demonstrate an objective improvement in time and technical performance of the arterial switch procedure on 3-dimensional printed heart models. This supports the evidence that simulation in the form of deliberate practice with constructive, objective feedback is fundamental in the training of future congenital heart surgeons. These simulations and assessments should be incorporated to create structured, standardized training curricula within congenital heart surgery.