My watch says my heart rate is high or low
A heart rate alert means your rate stayed above or below a set number while you seemed to be resting. Here is what sets it off, when the watch number is wrong, and what to save for your visit.
From Dr. Kenny Civello, cardiologist and electrophysiologist
Your watch counts your pulse with a light sensor. When the count stays above or below a limit for about 10 minutes while you seem to be still, it lets you know. It cannot tell you why. Most alerts have a simple reason. Some point to a rhythm worth checking.
What is normal
For most adults at rest, a rate between about 50 and 100 is normal. Fit people and people taking some heart medicines often run lower.
Low is often fine
Your rate falls when you sleep. In athletes it can rest near 40. A low rate matters most when it comes with dizziness, fainting, or feeling worn out.
High has many causes
Fever, illness, pain, stress, and some medicines raise your rate. So can a fast rhythm problem like AFib or SVT. A tracing tells them apart.
If a high or low heart rate comes with fainting, chest pain, shortness of breath, or any other symptom that worries you, call 911. Do not wait to see what your watch says next.
Why the watch waits until you are still
Your rate is supposed to rise when you move. A fast rate on a walk means nothing. A fast rate while you sit on the couch might. So most watches only check against your limits after about 10 minutes without much movement.
Why did my watch alert me?
Check anything that was true when the alert came. Nothing you enter leaves this device.
When the watch number is wrong
At rest, wrist sensors count normal heartbeats well. They have trouble in a few cases.
Movement and a loose band
Light leaking under the watch or a moving arm can give a reading that is too high or too low. Snug the band and check again while still.
AFib
In AFib, some beats are too weak to reach the wrist. In studies, watches counted fewer beats than an ECG, and the gap grew as the true rate rose. Your watch can show a normal number while your heart is beating fast.
Extra beats
An early extra beat may not push enough blood to feel at the wrist. The watch can miss it and show a rate lower than your heart's true rate.
Cold hands and tattoos
Less blood flow to the skin, or ink under the sensor, can weaken the signal the watch reads.
How to check the number yourself
Sit still for a few minutes. Find the pulse at your wrist or neck and count it for 30 seconds, then double it. If your watch can record an ECG, record one. The ECG counts the electrical beats directly, so it is more reliable than the light sensor when the rhythm is irregular.
Heart rate alerts by brand
Most watches let you pick the limits. Settings can change with updates.
| Device | When it checks | Where to set it |
|---|---|---|
| Apple Watch | After at least 10 minutes without much movement. You choose the high and low limits. Low Power Mode turns alerts off. | iPhone Watch app, then Heart |
| Samsung Galaxy Watch | While you rest. Heart rate has to be set to measure continuously. | Samsung Health, then Settings, then Heart rate |
| Google Pixel Watch and Fitbit | When you seem inactive for at least 10 minutes. The starting limits depend on your age and resting rate. You can set your own. | Fitbit app heart rate settings |
| Garmin | After at least 10 minutes without activity. Low alerts are not sent during your sleep window. | Garmin Connect, heart rate alerts |
| Withings ScanWatch | Only during rest, and not during sleep. Limits can be custom or automatic, which adjusts to you after 30 days. | Withings app device settings |
Should I change my limits?
Ask us first. If your rate always runs low because you are fit or take a beta blocker, a lower limit can stop alerts that tell you nothing new. If you have a rhythm problem we are watching, we may want the alerts set a certain way.
Save it and bring it
A record of what happened is more useful than the alert alone.
Note the moment
Write down the time, what you were doing, and how you felt, even if you felt fine.
Record an ECG
If your watch has an ECG app, record one while the rate is still high or low. Sit still with your arms resting. See how to record a useful ECG.
Look at the trend
Your heart app shows your rate over the day. A single spike means less than a pattern that repeats.
Bring it to your visit
Have your notes, ECG PDFs, and a screenshot of the heart rate graph on your phone. We read the tracing itself, not just the number.
Common questions
My watch says my heart rate went into the 40s at night. Is that OK?
Often, yes. Your rate drops when you sleep, and fit people can rest in the 40s. Tell us if you feel dizzy, faint, or very tired during the day, or if you snore or stop breathing in your sleep. Sleep apnea can cause slow rates at night.
My resting heart rate has been creeping up. Should I worry?
Look for a reason first. Illness, poor sleep, alcohol, stress, and hard training all raise your resting rate for days at a time. If it stays up for weeks without a reason, mention it at your next visit.
Should I stop my beta blocker because my rate is low?
No. Do not stop or change a heart medicine on your own. A low rate is often the medicine doing its job. Bring your readings and we will decide together.
Why did I get a high alert when I was just sitting?
Many things raise your rate at rest, like stress, caffeine, a fever, or a full bladder. A sudden jump from normal to fast that starts and stops all at once can be a rhythm problem like SVT. An ECG recorded during it shows us which.
Is the alert an FDA cleared medical feature?
Heart rate alerts are not a diagnosis. They are a nudge to look. The ECG app on many watches is a separate feature that is FDA cleared. See My watch says I have AFib.
More on wearables
My watch says I have AFibMy watch ECG says inconclusiveIrregular rhythm notifications, explainedMy watch says I may have sleep apneaFDA cleared or wellness: what the label meansWhich wearable features are FDA clearedHow I choose the wearables I recommendFind the right wearableBest smartwatch for catching AFibBest smart ring for sleepBest home blood pressure monitorBest personal ECG without a smartwatchBest wearable for an older parentBest wearable for athletesBest wearable without a screenThis page is general education for my patients. It does not replace advice from your own doctor. Watch heart rate alerts are not a diagnosis. Device names are trademarks of their makers. This page is not affiliated with any of them.
Based on: Kusumoto FM, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. J Am Coll Cardiol. 2019. Page RL, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. J Am Coll Cardiol. 2016. Al-Kaisey AM, et al. Accuracy of wrist-worn heart rate monitors for rate control assessment in atrial fibrillation. Int J Cardiol. 2019.