Apple Watch stops measuring heart rate

Hello helpx,

Welcome to Apple Support Communities. 

We understand that your heart rate isn’t being recorded as expected during workouts. We are happy to help.

Please use these steps to calibrate your Apple Watch: Calibrate your Apple Watch for improved Workout and Activity accuracy - Apple Support

"Calibrate your Apple Watch

1. While wearing your Apple Watch, go to a flat, open outdoor area that offers good GPS reception and clear skies.
2. If you have Apple Watch Series 2 or later, you just need your Apple Watch.* If you have Apple Watch Series 1 or earlier, bring your iPhone for GPS. Hold your iPhone in your hand, or wear it on an armband or waistband.
3. Open the Workout app, then tap Outdoor Walk or Outdoor Run. To set a goal before starting, tap .
4. Walk or run at your normal pace for about 20 minutes.

If you don't have time to finish the workout, you can complete 20 minutes over multiple outdoor Workout sessions. If you work out at different speeds, you should also calibrate for 20 minutes at each of the speeds that you walk or run.

Whenever you walk or run outside using the above steps, your Apple Watch continues to calibrate the accelerometer by learning your stride length at different speeds. Calibration can also improve the accuracy of your calorie calculations in the Workout app, and the calorie, distance, Move, and Exercise calculations in the Activity app. "

We also want to ensure that you are using the latest watchOS and iOS versions on your devices. Please use the steps here to update your Apple Watch: Update your Apple Watch - Apple Support

"Update your Apple Watch using your iPhone

You can wait until Apple Watch notifies you when a new update is available. Tap Update Tonight in the notification, then go to your iPhone to confirm that you want to update overnight. At the end of the day, leave your Apple Watch and iPhone charging overnight so the update can complete.

Or you can update your Apple Watch with your iPhone manually:

1. On your iPhone, open the Apple Watch app, then tap the My Watch tab. 
2. Tap General > Software Update.
3. Download the update. If asked for your iPhone passcode or Apple Watch passcode, enter it. 
4. Wait for the progress wheel to appear on your Apple Watch. It could take from several minutes to an hour for the update to complete. "

Please use the steps here to update your iPhone: Update your iPhone or iPad - Apple Support

"Update your iPhone or iPad wirelessly

1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."

Let us know if you have further questions.

Take care.

Hey helpx,

Those steps were from the Apple Support article we provided.

If you're still having issues with the heart rate measuring, we'd advise to contact Apple Support, so they can take a closer look.

Apple Support

All the best.