Try again heart rate

Hi

Apple advises that, even under ideal conditions, Apple Watch may not be able to record a reliable heart rate reading every time for everybody.

Besides ensuring the correct fit and potential issues with wrist tattoos (both of were covered in your question), skin perfusion can also affect sensor performance:

Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support

It may otherwise help to follow these steps:

If you have not yet done so, update your iPhone and Apple Watch to the latest software, starting with your iPhone:

• Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support
• Update the software on your Apple Watch - Apple Support

Close certain apps and restart both your iPhone and your watch:

• Close the Watch app, Activity app and Health app (if open) on your iPhone:
  • Double-click the Home button, then swipe up on each app preview to close it.
• Turn both devices off together, then restart your iPhone first:
  • Restart your iPhone, iPad, or iPod touch - Apple Support
  • Restart your Apple Watch - Apple Support
    • Note that Apple advises that you should not force restart your watch unless it is unresponsive and cannot be restarted normally.

Unpair and re-pair your watch:

• The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app. Choose to Restore from Backup during set up. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support

If the issue then persists and you are concerned about a potential hardware defect, I suggest that you contact Apple Support (mail-in service may be available), make a Genius Bar reservation or visit an Apple Authorised Service Provider with a view to having your watch checked and, if recommended, serviced / replaced under warranty:

• Contact - Official Apple Support
• https://twitter.com/applesupport
• http://www.apple.com/retail/geniusbar/
• https://locate.apple.com

To check your warranty status:

https://checkcoverage.apple.com

Try not to reboot your watch too often, if it didn't work the first time, try next step.

Look in the Health App in your phone. Under "vitals" click on Heart Rate, under chart you should see "show all data", click on date. Do you see any readings there? You should see readings taken every 10 minutes.

If you don't I would erase and re-pair with phone. To erase go to the settings app on your watch. Under general, scroll to bottom and you will see option to erase.

The set up again.

You need to have both Heart Rate and Fitness Tracking enabled in the watch application for this to work consistently. No need to reset or un-pair your watch. If you disable Fitness Tracking the issue will reoccur.