Many of the features on Apple devices were initially used only in the United States, but international users can usually simply use the zone as the US, but not this time.
If you want to use this feature, then your Apple Watch Series 4 must be a US version, and what Canadian, English, and Hong Kong versions will not work.
According to Apple, the ECG ECG app and irregular heart rate notifications are all regulatory features on Apple Watch. These two features have been approved by the US FDA for the De Novo classification and are available to users 22 years of age and older in the United States. Apple also mentioned that users who have already diagnosed atrial fibrillation should not use the app.
It is unclear whether the feature will expand to the world in the future, but there are rumors that Canada may be the next country. Apple's AW4 is sold worldwide, all with the heart sensor necessary for ECG functionality, but requires software activation.