HRV has long been recognized as a marker for autonomic nervous system activity. The autonomic (parasympathetic and sympathetic) nervous systems as well as hormonal factors provide the main input to the heart’s pacemaker, and the beat-to-beat interval variability is a reflection of the balance between these two.

Clinical research has documented reduction in HRV (decreased variability) in various disease states. Papers published in veterinary journals have shown that reduction in HRV is associated with heart diseases, sepsis, diabetes, obesity, and more. HRV has also been shown to be reduced in states of chronic pain and stress in humans and lab animals. It is the first objective, remote, non-invasive, quantifiable marker for pain.