**Abstract** -------- **Objective:** Relationship quality is one of the most consistent psychosocial predictors of physical and mental health. Yet, little research examines relationship types or support within the immediate context of acute health events. We tested the unexplored role that close others play in patients' experience of threat during evaluation for acute coronary syndrome (ACS) in the Emergency Department (ED), as well as the indirect effect of close others on ACS-induced posttraumatic stress disorder (PTSD). **Method:** Participants were 871 patients evaluated for ACS at an urban academic ED (60.86 years old; 54.08% male; 56.37% Hispanic, 19.86% Black, 16.65% White). Threat perceptions were assessed in-ED and median 3 days later. ACS-induced PTSD was assessed median 41 days later using the PTSD checklist cued to a specific stressor. Non-overlapping categories were created representing close others in the ED (i.e., spouse/significant other, child), non-close others (e.g., neighbor), or no one. **Results:** Patients who brought close others recalled experiencing greater threat in the ED: vs. no one, b = 0.11, p = .072; vs. non-close others, b = 0.16, p = .030. There was no direct effect of close others on ACS-induced PTSD; however, recalled threat mediated the effect of close others on development of ACS-induced PTSD, ps < .05. **Conclusions:** Close others were associated with recalling greater threat during ED evaluation, which predicted ACS-induced PTSD. ACS-induced PTSD is associated with medication nonadherence, event recurrence, and mortality, highlighting the need to develop a greater understanding of the impact stressful medical environments have on patients and close others. **Keywords:** Acute coronary syndromeSocial supportPTSDPsychological stressClose relationships **Link:** https://www.sciencedirect.com/science/article/pii/S0163834318303281 **Citation:** Cornelius, T., Meli, L., Thorson, K. R., Chang, B. P., Edmondson, D., & West, T. V. (2019). Bringing close others to the emergency department for an acute coronary event is associated with increased patient perception of threat. General Hospital Psychiatry, 56, 42-49. doi: 10.1016/j.genhosppsych.2018.12.002