Though existing research is sparse, studies investigating the effects of behavioral treatment on heart rate variability suggest that exposure and mindfulness-based treatments increase heart rate variability. Increases in resting heart rate variability were found following successful CBT for panic disorder (Craske, Lang, Aikins, &Mystkowski, 2005) and PTSD (Garakani et al., 2009), and after mindfulness-based treatment for substance use (Brewer et al., 2009). These findings suggest that low heart rate variability may be targeted by strategies in CBT and ACT. One small study found that individuals who were unresponsive to exposure therapy for flight phobia had higher baseline heart rate variability (Bornas, del Amo, Tortella-Feliu, & Llabres, 2012), supporting the notion that targeting emotion regulation may be more effective for individuals with low, rather than high, heart rate variability. However, no studies to our knowledge have examined heart rate variability as a predictor or moderator of outcome from CBT or ACT.