Thanks for asking about the new ECG feature.
Check here for availability in your region: ECG
ECG will not work on beta versions of watchOS or iOS and requires the current version of iOS and watchOS.
For additional help with the ECG feature on your Apple Watch, take a look at these articles.
Heart rate notifications on your Apple Watch - Apple Support
Taking an ECG with the ECG app on Apple Watch Series 4 - Apple Support
If you have any other questions please reach out to our team here: https://apple.co/HeartFeatures. If you believe that you are experiencing a medical emergency, please dial your local emergency services.