The highly anticipated ECG feature of the Apple Watch Series 4 is slated to be released with WatchOS 5.1.2. The news comes via MacRumors who obtained internal Apple Store training documents.
The documents state that the ECG app will available only in the United States initially as it is a regulated app. It must be cleared by local health authorities prior to being available in specific countries or regions. The FDA has approved the feature here in the United States.