Basically, you’ll need your iPhone to set up your Apple Watch’s ECG feature. After downloading and installing iOS 12.1.1 and watchOS 5.1.2, there will be a new popup pane that appears when you first open the Health app on iOS.
Tap on Set Up ECG App and follow the instructions to set it up. The Health app will ask you for your date of birth and also notify you of the various results that the ECG app will take in. Eventually, you’ll be asked to take a first ECG reading. Which brings us to the next slide…