Objective: Emergency physicians are challenged to efficiently and reliably risk stratify patients presenting with chest pain (CP) to optimize diagnostic testing and avoid unnecessary hospital admissions. The objective of our study was to evaluate the impact of a HEART score-based decision aid (HSDA) integrated in the electronic health record on coronary computed tomography angiography (CCTA) utilization and diagnostic yield in adult emergency department (ED) CP patients with suspected acute coronary syndrome. Methods: We conducted a before and after study to determine whether implementation of a mandatory computerized HSDA would reduce CCTA utilization in ED CP patients and improve the diagnostic yield of obstructive coronary artery disease (CAD) (≥50%). We included all adult ED CP patients with suspected acute coronary syndrome during the first 6 months of 2018 (before) and 2020 (after) at a large academic center. CCTA utilization and obstructive CAD yield were compared in patients before and after implementing the HSDA using χ 2 tests. Secondarily, we assessed the association of HEART scores and CCTA results. Results: Of the 3095 CP patients during the before study period, 733 underwent CCTA. Of the 2692 CP patients during the after study period, 339 underwent CCTA. CCTA utilization before and after HSDA was 23.4% [95% confidence interval (95% CI), 22.2-25.2] and 12.6% (95% CI, 11.4-13.0), respectively; mean difference was 11.1% (95% CI, 0.9-13.0). Among 1072 patients undergoing CCTA, mean (SD) age and percent females before versus after HSDA were 54 (11) versus 56 (11) years and 50% versus 49%, respectively. We included 1014 patients (686 before and 328 after) for the yield analysis. Obstructive CAD was present in 15% (95% CI, 12.7-17.9) and 20.1% (95% CI, 16.1-24.7) before and after HSDA, respectively; mean difference was 4.9% (95% CI, 0.1-10.1). Conclusions: Implementation of a mandatory electronic health record HSDA aid reduced ED CCTA utilization by half and improved the diagnostic yield.