- Background: Spectral analysis of heart rate variability has recently been shown to be a reliable noninvasive test for quantitative assessment of cardiovascular autonomic regulatory responses, providing a dynamic map of sympathetic and parasympathetic interaction. In a prior study exploring the state of hyperarousal characterizing the posttraumatic stress disorder (PTSD) syndrome, the authors described standardized heart rate analysis carried out in 9 PTSD patients at rest, which demonstrated clear-cut evidence of a baseline autonomic hyperarousal state. Methods: To examine the dynamics of this hyperarousal state, standardized heart rate analysis was carried out in 9 PTSD patients compared to a matched control group of 9 healthy volunteers. Twenty-minute recordings of electrocardiogram in response to a trauma-related cue as opposed to a resting state were performed and analyzed. The PTSD patients were asked to recount the presumed triggering traumatic event, and the control subjects recounted a significant stressful negative life event. Results: Our results show that, whereas the control subjects demonstrated significant autonomic responses to the stressogenic stimulus supplied by the recounting of a major stressful experience, the PTSD patients demonstrated almost no autonomic response to the recounting of the triggering stressful event. The PTSD patients demonstrated a degree of autonomic dysregulation at rest which was comparable to that seen in the control subjects’ reaction to the stress model. Conclusions: The lack of response to the stress model applied in the study appears to imply that PTSD patients experience so great a degree of autonomic hyperactivation at rest, that they are unable to marshal a further stress response to the recounting of the triggering trauma, as compared to control subjects.