EMDR combines stimuli that evoke divided attention--e.g. eye movements--with exposure to traumatic memories. Our objective was to investigate psycho-physiological correlates of EMDR during treatment sessions. A total of 55 treatment sessions from 10 patients with PTSD was monitored applying impedance cardiography. Onset of every stimulation/exposure period (n=811) was marked and effects within and across stimulation sets on heart rate (HR), heart rate variability (HRV), pre-ejection period (PEP) and respiration rate were examined. At stimulation onsets a sharp increase of HRV and a significant decrease of HR was noticed indicating de-arousal. During ongoing stimulation, PEP and HRV decreased significantly while respiration rate significantly increased, indicating stress-related arousal. However, across entire sessions a significant decrease of psycho-physiological activity was noticed, evidenced by progressively decreasing HR and increasing HRV. These findings suggest that EMDR is associated with patterns of autonomic activity associated with substantial psycho-physiological de-arousal over time.