Heart-rate-variability biofeedback is slow breathing with a readout: you breathe at roughly six breaths a minute while a sensor shows your heart rate rising and falling with each breath, and you learn to make that swing as large and smooth as you can. The book's Chapter 5 cites the physiology (Vaschillo, Lehrer and Gevirtz). The clinical trials have since been pooled several times.
For stress and anxiety, 24 studies totaling 484 people gave a between-groups effect of about 0.8, which is large by the standards of this field. For depressive symptoms, 14 randomized trials with 794 participants gave a medium effect of about 0.4. The broadest review, 58 studies across every outcome anyone had measured, found a small-to-moderate benefit overall, largest for anxiety, depression, anger, and athletic or artistic performance, and smallest for PTSD, sleep, and quality of life. A 2026 Australian trial in 73 people with both PTSD and chronic pain found a 24 percent drop in PTSD scores after six weeks, against no change on a waitlist.
The limits are the usual ones. Biofeedback trials are hard to blind, waitlists make generous comparisons, and the device is doing some of the work by holding your attention. You can do the breathing without the sensor; the sensor mainly tells you that you are doing it. The book's version is six breaths a minute, with the exhale slightly longer than the inhale.
The studies
Goessl VC, Curtiss JE, Hofmann SG. The effect of heart rate variability biofeedback training on stress and anxiety: a meta-analysis. Psychological Medicine 47(15), 2017, 2578–2586. Read the abstract
- Sample
- 24 studies, 484 participants
- Design
- Random-effects meta-analysis.
- Found
- Within-group effect g = 0.81; against controls g = 0.83. Not moderated by study year, risk of bias, number of sessions, or whether participants had an anxiety disorder.
- Limits
- The authors themselves call for more well-controlled studies.
Pizzoli SFM, Marzorati C, Gatti D, Monzani D, Mazzocco K, Pravettoni G. A meta-analysis on heart rate variability biofeedback and depressive symptoms. Scientific Reports 11, 2021, 6650. Read the abstract
- Sample
- 14 RCTs, 794 participants
- Design
- Random-effects meta-analysis of randomized trials in adults.
- Found
- Medium effect on depressive symptoms, g = 0.38.
- Limits
- Year of publication and choice of questionnaire moderated the effect; samples spanned many medical and psychiatric conditions.
Lehrer P, Kaur K, Sharma A, et al. Heart rate variability biofeedback improves emotional and physical health and performance: a systematic review and meta analysis. Applied Psychophysiology and Biofeedback 45(3), 2020, 109–129. Read the abstract
- Sample
- 58 studies
- Design
- Meta-analysis across all outcomes studied.
- Found
- Small-to-moderate effect favoring biofeedback, no different from other effective treatments; largest for anxiety, depression, anger and performance, smallest for PTSD, sleep and quality of life.
- Limits
- Few studies per outcome; effects larger against inactive than active controls. The lead author is a developer of the method.
Chadwick, Tatschl, Fujiyama, Drummond, Mathersul. Heart rate variability biofeedback improves co-occurring posttraumatic stress disorder and chronic pain symptoms: a randomised waitlist-controlled trial. Journal of Affective Disorders 394 (Pt A), 2026, 120558. Read the abstract
- Sample
- 73
- Design
- Six weeks of HRV biofeedback versus waitlist in adults meeting criteria for both PTSD and chronic pain.
- Found
- PTSD Checklist scores fell 24.3 percent (d = −1.89) with improvement across all symptom clusters; no significant change on the waitlist.
- Limits
- Waitlist comparison; mostly women; single country.
Where this lands in the book
Techniques
Rooms
Two rules, no exceptions
Never practice any technique on this site while you are driving, operating machinery, or doing anything that needs your full attention. The slow ones can make you drowsy, faster than you’d expect. And never practice a breath-hold, bellows breath, or any vigorous breathing in or near water. Read Before you begin for the doctor’s list and the rest.
Verdict scale: Science means trials or meta-analyses with consistent findings; Promising means real trials that are small, few, or unreplicated; Mixed means the studies point both ways; Mechanism means it shows how something works in the body, not that it helps in life. Checked against the published abstracts in October 2026. Not medical advice.