The next watchOS update will reportedly include the ECG app
 

One of the main features Apple announced for Apple Watch Series 4 was an electrocardiogram app, which could help you detect an irregular heart rhythm. While it wasn't included with the Watch Series 4 at release, nor in last month's watchOS update, it...

https://www.engadget.com/2018/11/28/...m-app-watchos/