BACKGROUND: Hands-on surgical simulation has been sought to address training limitations within congenital heart surgery (CHS). However, there is a need for objective assessment methods to measure surgeons' performance to justify its global adoption. This study aimed to validate a procedure-specific assessment tool for the simulation of the arterial switch operation on 3D-printed models and to evaluate the consistency of scoring among evaluators with different levels of experience in CHS. METHODS: Five "expert" and 5 "junior" surgeons performed the arterial switch procedure on 3D-printed models with transposition of the great arteries during 2 hands-on surgical training courses. Their performance was retrospectively assessed by 9 evaluators with varying experience in CHS (staff surgeons, resident surgeons, and non-MD raters). Assessments were done using 2 assessment tools: the Hands-On Surgical Training-Congenital Heart Surgery (HOST-CHS) assessment tool and the global rating scale (GRS). RESULTS: The HOST-CHS tool showed a higher interrater and intrarater reliability compared with the GRS. Total scores for expert surgeons were highly consistent across all evaluators. Non-MD raters' total scores for junior surgeons were slightly higher than those of residents and staff evaluators. All grades of evaluator were able to discriminate between junior and expert surgeons. CONCLUSIONS: This study demonstrates the development and validation of an objective, procedure-specific assessment tool for the arterial switch operation with consistency among evaluators with different experience. There is now a platform for quantifying and accurately evaluating performance, which will be highly beneficial in training and developing the next generation of congenital heart surgeons.