Objectives: Significant practice variation is seen in the management of syncope in the emergency department (ED). We sought to evaluate the feasibility of performing a randomized controlled trial of a shared decision making (SDM) tool for low-to-intermediate–risk syncope patients presenting to the ED. Methods: We performed a randomized controlled trial of adults (≥30 years) with unexplained syncope who presented to an academic ED in the United States. Patients with a serious diagnosis identified in the ED were excluded. Patients were randomized, 1:1, to receive either usual care or a personalized syncope decision aid (SynDA) meant to facilitate SDM. Our primary outcome was feasibility, i.e., ability to enroll 50 patients in 24 months. Secondary outcomes included patient knowledge, involvement (measured with OPTION-5), rating of care, and clinical outcomes at 30 days post-ED visit. Results: After screening 351 patients, we enrolled 50 participants with unexplained syncope from January 2017 to January 2019. The most common reason for exclusion was lack of clinical equipoise to justify SDM (n = 124). Patients in the SynDA arm tended to have greater patient involvement, as shown by higher OPTION-5 scores: 52/100 versus 27/100 (between-group difference = −25.4, 95% confidence interval = −13.5 to −37.3). Both groups had similar levels of clinical knowledge, ratings of care, and serious clinical outcomes at 30 days. Conclusions: Among ED patients with unexplained syncope, a randomized controlled trial of a shared decision-making tool is feasible. Although this study was not powered to detect differences in clinical outcomes, it demonstrates feasibility, while providing key lessons and effect sizes that could inform the design of future SDM trials.