Can my apple watch 4 with model A1977 use the ECG now? Or i need to wait the new update?

Thanks for asking about the new ECG feature.

Check here for availability in your region: ECG

ECG requires the current non-beta 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.

Take care

If you are not using beta software on the phone you should be able to use the ECG app with the latest watchOS.