© 2017, © The Author(s) 2017. Background. We test the hypotheses that use of the Chest Pain Choice (CPC) decision aid (DA) would be similarly effective in potentially vulnerable subgroups but increase knowledge more in patients with higher education and trust in physicians more in patients from racial minority groups. Methods. This was a secondary analysis of a multicenter randomized trial in adults with chest pain potentially due to acute coronary syndrome. The trial compared an intervention group engaged in shared decision making (SDM) using CPC to a control group receiving usual care (UC). We assessed for subgroup effects based on age, sex, race, income, insurance, education, literacy, and numeracy. We dichotomized each characteristic and tested for interactions using regression models with indicators for arm assignment and study site. Results. Of 898 patients (451 DA, 447 UC), over 50% were female, over one-third were black, nearly one-third had a high school education or less, and over 60% had “low” health literacy. The DA did not increase knowledge more in patients with higher education (P for interaction = 0.06) but did increase knowledge more in the “typical” than in the “low” numeracy subgroup (10.6% v. 4.7%, absolute difference [AD] = 5.9%, P for interaction = 0.025). The DA did not significantly increase patient trust in physicians in racial minorities (P for interaction = 0.06) but did increase trust more in patients with “low” literacy compared with those with “typical” literacy (3.7% v. –1.4%, AD = 5.1, P for interaction = 0.011). Conclusions. CPC benefited all sociodemographic groups to a similar extent, with greater knowledge transfer in patients with higher numeracy and greater physician trust in patients with “low” health literacy. Tailoring SDM interventions to patient characteristics may be necessary for optimal effectiveness.