This small-scale study investigates the relationships between the heart rate of motor vehicle accident survivors presenting in the emergency department (ED) and acute stress disorder (ASD) and posttraumatic stress disorder (PTSD) symptom severity. It also examines the relationships between the survivor's heart rate in the ED and peritraumatic dissociation and peritraumatic distress reported 2 weeks posttrauma. Fifty motor vehicle accident (MVA) survivors were assessed 2 weeks, 1 (N = 42), 3 (N = 37), and 6 months (N = 37) post-MVA. The heart rate in the ED predicted self-reported ASD symptom severity and clinician-rated PTSD symptom severity at 6 months but not at 1 or 3 months. Survivors' heart rate in the ED was significantly correlated with peritraumatic dissociation but not peritraumatic distress. These findings support the role of elevated ED heart rate as a predictor of both ASD and chronic PTSD symptom severity and may help to clarify the discrepant findings of previous research.