Your heart rate is more uneven than you think. This is what it says about your health

Micro-fluctuations in the time between heartbeats are proving a helpful indicator of mental health, stress levels and exercise capacity. They could even provide insight into how well you are ageing.

Artem Kirillov is not, by nature, the kind of person to take it easy. “I prefer to push myself further, even if I feel a bit off,” says Kirillov, who is 40, lives in London and works in health tech. For a long time, even as a recreational exerciser, he discounted the need for rest days and pushed through fatigue at the gym, believing that more time spent training automatically meant better results.

Until, that is, he began paying attention to heart rate variability, one of the many health data points tracked by his smartwatch. A more complex metric than heart rate – the number of times the heart beats per minute – heart rate variability reflects how the time between heartbeats fluctuates. A growing body of research suggests it’s an indicator of cardiovascular health, stress levels, exercise capacity and more, allowing dedicated trackers to make more informed decisions about their fitness regimes and lifestyles.

Now, if Kirillov is on the fence about whether it’s better to take a day off or grind it out in the gym, he consults his heart rate variability score. Since adopting that habit, “I feel like I’m in better balance with myself”, he says. He’s such a convert, he even launched an app dedicated to tracking stress using heart rate variability data.

As wearables become ever-more ubiquitous and research on heart variability accumulates, more people are joining Kirillov in keeping this score, says Deepak Bhatt, director of the Mount Sinai Fuster Heart Hospital in New York City, US.

But do you actually need to track heart rate variability, and what can you learn if you do? Here’s what to know.

What is heart rate variability?

“You want a heart to beat more or less regularly,” Bhatt says. When the heart beats extremely irregularly, it’s classified as an arrhythmia, which in serious cases can result in complications such as stroke or heart failure.

But even a healthy heart has some variation in the time between its beats, Bhatt says. These variations are tiny, measured on the order of milliseconds (one millisecond is a thousandth of a second). And when looking at changes on this scale, “a higher variability, in general, is considered better” than a lower one, Bhatt says.

There’s no single ideal heart rate variability score, as it varies by age, fitness level, sex, tracking device and calculation method. But one wearable brand says the average score for its users, who tend to be active and health-conscious, is 65 milliseconds for men and 62 milliseconds for women. And there’s huge variation by age group: the average score for 25-year-olds is 78, compared to 44 for 55-year-olds.

While the maths behind these numbers is complex, you can think of them as approximations of the average fluctuation in the time intervals between heartbeats in milliseconds.

Shooting for a high heart rate variability may seem counterintuitive, since a low resting heart rate suggests someone has good cardiovascular fitness. High heart rate variability, though, is a way to measure how well your nervous system is cycling between its “fight-or-flight” stress response and its “rest-and-digest” relaxation response.

Here’s how it works. If you need to outrun a predator – or just go out for a jog – your nervous system triggers a range of physiologic responses that give you energy and acuity. Among other effects, your heart rate rises. When it does, your heart rate variability drops because the heart has to keep beating at a fast and steady pace to sustain you.

When you’re back at rest, the nervous system should calm everything back down. In this relaxed state, your heart rate naturally beats at a more variable pace – for example, speeding up a little when you inhale, then slowing down when you exhale.

A high average heart rate variability “shows that your system can, when it needs to, quickly change heart rate and blood pressure to match the environment or to match the circumstances”, says Dennis Larsson, a postdoctoral research fellow at Kiel University in Germany who has studied heart rate variability. This suggests it can spring into action when something is stressful but relax again when something doesn’t have to be stressful.

A low heart rate variability, on the other hand, suggests you’re getting stuck in one state – most commonly, that stressed-out fight-or-flight mode. Modern life, after all, is full of stressors that can rev up the nervous system, from traffic jams to work deadlines.

Consider an automated temperature control system in a building. Ideally, the system should adjust to small variations in outdoor climate to keep you comfortable inside. If the system gets stuck at one temperature – blasting at high heat even on an unseasonably warm spring day, say – that’s not a good thing. You’ll be left sweltering (and tempted to call the repairman). Your body isn’t so different. When your system is in proper balance, it should be highly responsive to different internal and external cues.

What heart rate variability says about your health

Cardiologists use heart rate variability, along with other metrics, to assess how well your heart is working and look for warning signs of disease. Bhatt’s research, for example, suggests heart rate variability data can help identify atrial fibrillation, a potentially serious form of arrhythmia.

Some athletes also use their heart rate variability score to assess how well their body is recovering from strenuous physical efforts. Ideally, heart rate variability should dip during a hard workout, then rise again afterwards. If it stays depressed for days after a gym session, that suggests the body needs extra rest to get back to full strength.

Because it reflects stress and nervous system health, heart rate variability also seems to be a strong indicator of mental health. A 2023 research review found that, across most studies, heart rate variability tends to be lower among people with anxiety and depression, compared to people without these diagnoses. Someone with clinical anxiety is in “a continuous state of stress or duress,” says Larsson. “There, you see a continuously reduced level of heart rate variability,” signalling that their body is stuck in fight-or-flight mode.

Other research has found that people with conditions including post-traumatic stress disorder, dementia and schizophrenia often have lower-than-normal scores. In some cases, when people with psychiatric diagnoses receive treatments such as psychotherapy or transcranial magnetic stimulation, their heart rate variability subsequently improves, suggesting the nervous system is working better, according to a 2025 research review. (Other studies, however, have shown that psychiatric treatments, such as certain antidepressant medications, can lower heart rate variability as part of their broader effects on the nervous system.)

These conclusions must be taken with caution, however. Many studies of heart rate variability and mental health are small, unreplicated and subject to a common problem in the field: there are lots of ways to measure heart rate variability – monitoring people for five minutes compared to a full day, say.

Beyond mental health, heart rate variability might even provide insight into how well you are ageing. Being chronically stressed fuels inflammation, studies show, and inflammation plays a role in numerous chronic diseases. Since heart rate variability is one way to assess how well the body is handling stress, it could be used to predict inflammation levels and, thus, risk for ageing-related disease, argued one 2024 research review.

Could heart rate variability be a treatment target?

Some researchers think that purposely manipulating heart rate variability could be an effective way to treat various mental and physical health conditions.

Breathwork is perhaps the most accessible way to regulate your heart rate variability, because the heart naturally speeds up and slows down in time with your inhalations and exhalations, says Tim Herzog, a licensed clinical psychologist in Virginia, US, who is also a certified biofeedback practitioner. Herzog recommends that people set aside about 20 minutes, twice a day, to practice slow, mindful breathing – like inhaling for four seconds, then exhaling for six.

More research is needed, though. There are different ways of practising breathwork besides this, and experts need to work out which is best. Still, some studies suggest it’s a promising path to follow. Researchers have found that when people with mental health conditions, including PTSD and depression, practice structured breathing meant to boost their heart rate variability scores, their mental health symptoms tend to decrease.

Other studies outside the mental health realm – albeit mostly small and preliminary ones – have shown that such breathwork programmes can result in better sleep, lower blood pressure and lessened chronic pain.

Not all scientists are convinced that heart rate variability needs to be purposely altered, though.

Larsson considers heart rate variability “a metric to look at what the underlying conditions are”, but not something that needs to be directly treated.

Bhatt agrees. Heart rate variability often improves when people start adopting healthy behaviours, such as exercising or getting consistent sleep, but “it’s a chicken-and-egg sort of thing”, he says. “Is the heart rate variability improving, per se, what’s important? Or is it what led to it improving?”

How should you track heart rate variability?

Lots of consumer wearables track heart rate variability. But some are dramatically more accurate than others, cautions Karin Steere, an associate professor at the University of Puget Sound in Washington, US. Her research suggests devices that fasten around the chest do a better job than more common styles worn around the wrist.

No matter what kind of wearable you use, she says, remember that heart rate variability is most useful when assessed over time, not at a single moment. Heart rate variability is supposed to change throughout the day. When you’re out for a run, your heart rate variability will naturally look different from what it does at rest. So, looking at a single score will tell you less than watching how it changes over time.

“Every morning, take your HRV, see what that looks like, and then think about what just preceded that,” Steere recommends. “Did I have a really good night’s sleep? Did I have a couple glasses of wine the night before?”

Over time, as you get a sense of your baseline and how your heart rate variability changes depending on your health and behaviour, you can use that data to help you make decisions and track progress, Herzog says.

Maybe you were already feeling sluggish and your heart rate variability data drives home that your system is overtaxed and needs rest. Or perhaps you’ve just started a new exercise regimen but aren’t seeing physical results yet. Since heart rate variability tends to improve with exercise, a higher score could encourage you that your gym sessions really are working. Tracking it, if anything, “ends up really enhancing subjective awareness”, Herzog says.

And if all of this sounds overwhelming? Don’t let your heart skip a beat over it, Bhatt says.

Heart rate variability can be helpful or interesting for people who are highly motivated to track their health data.

But, in Bhatt’s view, there are plenty of metrics that are easier to understand – and probably more important – than variability, such as heart rate, blood pressure, weight, waist circumference and cholesterol levels. “Every adult should know those numbers,” Bhatt says, “and most people aren’t even doing that”.