Heart rate variability is a physiological measure associated with autonomic nervous system activity. Thisstudy hypothesized that lower pre-deployment HRV would be associated with higher post-deploymentpost-traumatic stress disorder (PTSD) symptoms. Three-hundred-forty-three Army National Guard sol-diers enrolled in the Warriors Achieving Resilience (WAR) study were analyzed. The primary outcomewas PTSD symptom severity using the PTSD Checklist..