**Abstract**

This chapter on heart rate variability (HRV) presents a view based on our published data that HRV profiles in depression and anxiety show differences and can be used for the differentiation of these two disorders in clinical practices. Characteristic HRV profiles in depression and anxiety are revealed by measurements incorporating task load. Analysis of two frequency-domain HRV parameters, low frequency (LF) and high frequency (HF), together with heart rate (HR) itself measured at rest (Rest), during the task load (Task), and at rest after the task (After) enables the evaluation of the autonomic regulation in response to behavioral changes with different stress levels. LF is the heart rate modulation related to blood pressure changes to stabilize circulation. HF is related to breathing rhythm and reflects parasympathetic activity. It has been indicated that LF, HF, their ratio LF/HF and HR in depression and anxiety show characteristic dysregulations during Rest, Task and After. These HRV profiles are useful for understanding the pathophysiology of the disorders.

**Keywords:** heart rate variability, baseline and reactivity, autonomic dysregulation, depression, anxiety
