Breathing and heart rate variability (HRV): what it means

What is heart rate variability?

Your heart doesn’t beat like a metronome. Even at rest, the gap between beats changes slightly from one beat to the next. Heart rate variability, or HRV, is a measure of how much it changes.

Much of that variation comes from your breathing. As you breathe in, your heart speeds up a little; as you breathe out, it slows down. Doctors call this respiratory sinus arrhythmia, and it is a normal, healthy pattern, strongest in young, fit people. The slowing on the out-breath is controlled by the vagus nerve, so HRV is often used as a rough window into how active the calming side of your nervous system is.

Why slow breathing raises it

When you breathe at around six breaths a minute, something useful happens. The rise and fall of your heart rate with each breath lines up with a second rhythm, the reflex that keeps your blood pressure steady. The two reinforce each other, and the swings in heart rate become much larger. This is called breathing at your resonance frequency, and it is where resonance breathing gets its name. Most people’s resonance frequency is between about 4.5 and 7 breaths a minute.

What the research shows

The effect of slow breathing on HRV is one of the most consistent findings in breathing research. A 2022 review of 223 studies found that slow breathing raised the vagal measures of HRV during practice, straight after a session and after programmes lasting weeks. That is why we grade this benefit as strong.

The bigger question is what it means for your health. In long-term studies, people with low resting HRV are more likely to develop heart disease: a 2013 review of eight studies with nearly 22,000 people found a 32% to 45% higher risk of a first cardiovascular event in those with the lowest HRV. But those studies can’t show that raising HRV with breathing exercises lowers that risk; low HRV may simply be a sign of other problems, such as poor fitness or illness. Trials of HRV biofeedback, which trains resonance breathing using a heart rate sensor, have found falls in stress and anxiety, but they are mostly small.

So: slow breathing reliably raises HRV. Whether that improves your long-term health is not yet known.

What about the HRV on my watch?

Many watches and rings now give an overnight or morning HRV figure. These can be useful for spotting your own trends, such as lower readings after alcohol, poor sleep or when you’re getting ill. But devices measure HRV in different ways, so numbers can’t be compared between brands, and day-to-day changes are normal. Don’t chase a number, and don’t worry about a single low reading.

If you want to use breathing to work on HRV, practise resonance breathing for 10 to 20 minutes a day, and look at your trend over weeks rather than days.