Apple Watch stopped measuring heart 2 days ago

Hello tkmphx1,

Welcome to Apple Support Communities. 

We understand that your Apple Watch is no longer recording your heart rate. We are happy to help.

Please use the steps here to monitor your heart rate: Monitor your heart rate with Apple Watch - Apple Support

"When Apple Watch measure your heart rate

When you use the Workout app, Apple Watch measures your heart rate continuously during the workout and for 3 minutes after the workout ends to determine a workout recovery rate. If you don't see your heart rate, check your settings.

This information, as well as other data it collects, helps Apple Watch estimate how many calories you’ve burned. In addition, Apple Watch measures your heart rate throughout the day when you’re still, and periodically when you’re walking (Apple Watch Series 1 or later). Since Apple Watch takes these background readings based on your activity, the time between these measurements will vary. Apple Watch also calculates a daily resting rate and walking average by correlating background heart rate readings with accelerometer data when sufficient background readings are available.1 You can control which third-party apps have access to your health data from the Health app in Sources.

For best results

Start with a good fit. Even under ideal conditions, Apple Watch may not be able to get a reliable heart rate reading every time for everybody. And for a small percentage of users, various factors may make it impossible to get any heart rate reading at all. But there are things you can do to help Apple Watch get the most consistent and best heart rate readings possible. Learn what else affects your reading."

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

"Check your settings

To make sure that your Apple Watch can get the information it needs, check these settings on your iPhone:

1. On your iPhone, open the Settings app.
2. Tap Privacy & Security > Location Services. 
3. Make sure that Location Services is turned on.
4. Scroll down, then tap System Services. 
5. Make sure that Motion Calibration & Distance is turned on.
6. Continue with the steps below.

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."

These steps may help. Let us know if you have further questions.

Take care.