Apple has confirmed that WatchOS 5.1.2 will be released later this morning. The new update will bring the much anticipated Electrocardiogram feature to the Apple Watch Series 4. It will also bring irregular heartbeat notifications to all supported Watches.
The ECG feature was one of the most touted features at the launch of the Apple Watch Series 4 back in September but has been missing as Apple continue to tweak on it to get it perfected. That exercise appears to be completed. WatchOS 5.1.2 has been in beta for a little over a month now and rumors have been pointing to the ECG feature being released with it almost since the beginning.
If you have an Apple Watch Series 4, after you update to WatchOS 5.1.2, you will be able to take a ECG using the app and holding the Digital Crown on your watch. This is done through the array of sensors on the back of the Watch. It is that set of sensors that limits the ECG feature to the Series 4.
As for the Series 1, 2, and 3, you are not out completely. With 5.1.2 you will also get notifications of irregular heart rhythm. This can be an indicator of more serious health and heart issues.
Typically, Apple releases firmware updates around 10:00 am Pacific time on their release dates. That should be the same here for this update to WatchOS. You will be able to check for the update after that time via the Watch app on your iPhone. Remember, to apply updates to your Apple Watch, it must have 80% remaining battery and be on its charger.