You may feel your heart racing occasionally throughout the day, signaling moments of stress or exertion. Along with blood pressure and cholesterol levels, understanding your heart rate and how it fluctuates can be an important indicator of heart health.

“Our heart rates are dynamic throughout the day,” says Dr. Corey Bradley, a cardiologist at NewYork-Presbyterian/Columbia University Irving Medical Center. “Heart rate variability is a sign of good cardiovascular health and fitness. Any sort of physiologic or psychologic stress can increase our heart rate. What’s important is not so much what your heart rate does in those moments of stress, but whether it’s recovering. When you’re coming down from those stressors, does your heart rate come down as well? If not, it can be a sign that perhaps something else is going on.”

Dr. Bradley shares more with Health Matters on normal resting heart rates, how to interpret data from smart devices, and what your numbers are telling you.

What is a heart rate, and what is a normal heart rate?

Dr. Bradley: Your heart rate is the number of beats your heart takes every minute (beats per minute, or BPM). In general, there’s a wide range for what we consider to be a normal, resting heart rate: between 60 and 100 BPM.

How can someone measure their heart rate?

Most people can measure their heart rate by checking their pulse at their wrist, placing two fingers between the bone and tendon. Count the number of beats in 15 seconds and multiply by four to calculate beats per minute.

A lot of wearable monitors such as smartwatches or rings measure your pulse from your wrist or finger. They’re a noninvasive way for doctors to get long-term data, if patients choose to share.

How accurate are smartwatches at measuring heart rate?

At rest, the accuracy of these devices is quite good. To approximate heart rate, most wearable devices rely on an optical sensor in the back that shines a light into your skin and measures the amount of light reflected to see how much oxygen is removed from your bloodstream and tissues. This does rely on the light being in a stationary place, so if you’re doing exercises that require you to move your arms a lot, like an elliptical or rowing machine, you may lose a little bit of accuracy.

There are also chest bands with electrodes that athletes can wear that measure heart rate during exercise.

What are exercise heart rate zones?

When people focus on zone training, often they target a specific goal, such as weight loss or endurance. There are five heart rate zones that tell you how hard you’re exercising and can indicate fat burning or other fitness benefits, such as improving speed.

They’re calculated based on a percentage of your maximum heart rate, which differs from person to person based on age. To find your maximum heart rate, subtract your age from 220.

What is heart rate variability?

Heart rate variability, or HRV, is the variation in time between your heart beats.

Is your heart rate changing throughout the day? Normal heart rate variability means that your heart rate can slow down when you’re at rest or when you’re sleeping, and then appropriately increases when you’re doing activity. That tells me that your heart’s electrical system is responding appropriately to stressors, but also that your heart is not under any more stress than it needs to be.

Heart rate fluctuation is normal and can be from a variety of things. Caffeine or exercise can increase your heart rate, and sometimes hot showers can as well because it causes blood vessels to dilate.

A slow, resting heart rate is normal, as long as you’re not feeling lightheaded or dizzy.

When is it time to see a doctor?

When people develop heart disease, their heart rate variability can diminish. Sometimes that means that their heart rate isn’t dropping when they sleep, or it’s harder for them to get their heart rate up. There are some medications, such as beta blockers, that appropriately blunt people’s heart rate variability and response to stressors.

Otherwise, drastic changes or low heart rate variability might indicate that you’re getting a little bit more out of shape, or perhaps have a disease process going on, so you always want to check with your health care provider.

Common conditions that can increase heart rate are anemia and iron deficiency. Thyroid disease can cause your heart rate to become too fast or too slow, and sometimes we can identify these conditions before symptoms have developed because people will notice these changes based off their resting heart rate.

Some smartwatches can give you an electrocardiogram analysis of your heart rhythm, which you can ask your doctor to review if you are seeing or feeling any irregular rhythms or palpitations.

If you’re using these devices, it’s a great starting point and can be empowering for people to see real-time results in the metrics, but it’s important to remember that they are validated for recreational use. If you notice a change and are experiencing symptoms, we always want that information to be verified by devices that are approved for medical use.