Where it comes from

Its link with survival emerged in studies of heart attack patients. In a 1978 study of 176 patients, those with more beat-to-beat variation on admission had lower hospital mortality. In 1987, among 808 heart attack survivors, those whose variation over 24 hours was below 50 milliseconds had 5.3 times the mortality of those above 100. A 1996 task force of European and North American cardiology societies then set standards for measuring it.

What it can and cannot tell you

Lower HRV is linked with age, heart disease and depression: in one meta-analysis, people with depression had lower HRV than healthy controls, and antidepressant treatment did not restore it. For an individual, the number is hard to read. Healthy adults differ enormously, a review of 44 studies with 21,438 people found, and HRV falls with age. Short recordings are not interchangeable with 24-hour ones, and higher is not always better, since some rhythm problems such as atrial fibrillation also raise it. In a small test of seven consumer devices against an electrocardiogram, the average error for one common HRV measure ranged from about 4 percent to more than 100 percent.

HRV biofeedback

HRV biofeedback uses real-time feedback to teach slow breathing that enlarges these beat-to-beat swings. Pooling 24 studies with 484 participants, a 2017 meta-analysis found that people reported markedly less stress and anxiety (an effect size, Hedges’ g, of 0.83 against control conditions), though the authors called for more well-controlled trials. Our research page summarizes that evidence as part of the somatic component of our program.

Related terms

Biological Age: what epigenetic clocks estimate, and their limits.

Somatic Experiencing: a body-oriented trauma therapy with a smaller evidence base.