Introduction: Post-operative (post-op) complete atrio-ventricular heart block (CAVB) occurs after 1% - 4% of pediatric cardiac operations. Current practice dictates implantation of permanent pacemaker (PPM) when post-op CAVB persists >9 days. We propose that earlier PPM implantation may be the most cost-effective methodology since patient costs increase with extended length of stay (LOS). Methods: Data on the probabilities of persistent post-op CAVB were extracted from published reports. No individual patient data were utilized during this study. This was utilized to create a decision-making model and a total cost analysis on post-op day 0 - 10 to determine the most cost-efficient day to implant a PPM. Cost variables included estimates of daily cardiac ICU care, cost of PPM implantation, LOS, cost related to possible superficial or deep infection based on published prevalence rates (2.3% and 4.9%, respectively) and need for explant due to deep infection or recovery of native conduction. The model assumes 5-day minimum LOS and 1 day increase in LOS with PPM implantation. Cost data were obtained from relevant billing codes and manufacturer list prices for PPM and leads. A secondary analysis evaluated probability of unnecessary PPMs implanted and excess costs. Results: Post-op day (POD) 4 is the lowest total cost of PPM implantation for post-op CAVB, even when accounting for possible risk of either superficial or deep infection. A one-way sensitivity analysis accounting for variability of cardiac ICU care costs between centers ranging from $3000 - $9000 per day consistently replicates POD 4 as the most cost-effective day for PPM implantation. Implant on POD 4 results in a 26% chance of unnecessary implantation. Conclusions: The most cost-efficient day for PPM implantation for post-op CAVB is post-op day 4, which results in a minimum total cost savings of $17,422 per patient. Added costs due to risk of superficial or deep infection are marginal due to low prevalence of post-operative infection in this population.