**2. Key concepts**

The chapter is organized into several sections. In Section 3, the role of HRV in autonomic cardiac control as it is found in normal adaptation is described. The specific topic headings in this section are: *Autonomic cardiac regulation; HRV and HRV coherence; Neurophysiological basis of HRV: polyvagal and neurovisceral; HRV and orienting; Executive control of attention and defense;* and *Autonomic cardiac regulation and fear.* In Section 4, the topic headings *Autonomic cardiac dysre‐ gulation in PTSD* and *PTSD and attention bias* discuss the derangement of normal ANS cardiac control by PTSD. Section 5 has only one topic heading titled *Applied psychophysiological therapy for PTSD and attention bias: HRV biofeedback* which presents the case that application of the HRVB intervention is intuitively and theoretically sound. In Section 6, *Models of Autonomic Dysregu‐ lation in PTSD* is a graphic representation of our ideas of how HRV influences orienting in normal and in the PTSD phenotype. In Section 7, the topic heading *Completed Research on HRVB* *and PTSD* and *Planned Research on HRVB and PTSD: The Action Cascade* details the work that has been done in our laboratory and the direction we are taking to further this important line of clinical research.
