Aims: Cardiac Implantable Electronic Devices (CIED) training for novice implanters typically occurs in vivo, varies across countries/institutions, and results in inconsistent skill levels. Proficiency-Based Progression (PBP) simulation training—requiring attainment of expert-derived performance benchmarks before clinical practice—reduced procedural errors by 61–77% compared with traditional simulation-based training (SBT) in randomised simulation trials. This study aimed to quantify clinical skill transfer in CIED implantation for the first time, comparing in vivo deviations from expert-agreed optimal technique in early-career implanters previously randomised to PBP versus SBT. Methods and results: Prospective observational cohort study following participants from a prior multinational randomised simulation trial to assess transfer of training to clinical practice. Early-career implanters (≥20 prior pacemaker/defibrillator cases; limited CRT first-operator experience) reported the implant technique they applied in their first two routine clinical cases within 30 days of training, using a validated standardised performance metrics form assessing surgical and lead implantation steps. The primary outcome was the mean percentage of deviations from optimal technique per participant. Of 30 randomised participants, 21 (70%) submitted 42 case reports (10 PBP, 11 SBT). Baseline characteristics were similar and case complexity did not differ between groups (p = 0.43). PBP trainees demonstrated 60% fewer procedural deviations than SBT trainees (mean [SD], 5.8% [3.8%] vs 14.4% [9.1%]; p = 0.013). Conclusion: Metrics-based PBP training was associated with significantly fewer procedural deviations from optimal CIED implant technique during early clinical practice compared with traditional simulation. These findings support benchmark-based simulation as a strategy to improve early clinical skill transfer in cardiac electrophysiology.