Background: The present study investigated the extent to which heart rate (HR) levels soon after a traumatic event predicted posttraumatic stress disorder (PTSD) symptom severity assessed 6 weeks and 6 months later in child trauma victims. Methods: Participants consisted of 82 children (56 boys, 26 girls) aged 8-18 who were admitted to a Midwestern trauma center. HR data were recorded from emergency medical services (EMS) records, upon admission to the emergency department (ED), for the first 20 minutes following admission, and upon discharge. Subsequent PTSD and depressive symptoms were assessed 6-weeks and 6-months post-trauma. Results: HR recorded during EMS transport was significantly correlated with PTSD symptoms at 6 weeks (r = 0.42) and at 6 months (r = 0.35). After removing the variance associated with demographic variables and depressive symptoms, HR during EMS transport and averaged over the first 20 minutes following admission significantly predicted 6-week PTSD symptoms. The first recorded EMS HR measure significantly predicted 6-month PTSD symptoms. HR averaged over the first 20 minutes of EMS transport and averaged over the first 20 minutes following admission marginally predicted 6-month PTSD symptoms (ps = 0.051 and 0.079, respectively). Conclusions: The present findings suggest that physiological arousal soon after a traumatic event may be associated with increased risk for the development of PTSD symptoms in child trauma victims. These findings provide preliminary support for the use of acute cardiovascular levels as markers of child trauma victims at higher risk of developing symptoms of PTSD.