For those who are just getting started with an Apple Watch, or those who have had one for a while but never used any of the heart rate features -- here's what you need to know.
Check your heart rate
You have a couple different options to check your heart rate using an Apple Watch. The quickest is to trigger Siri and ask "What's my heart rate?" The Heart Rate app will launch and present your current heart rate within a few seconds.
The other method to check your heart rate is to manually launch the Heart Rate app, either via the app icon or using the Heart Rate complication on a watch face.
The Heart Rate app on the watch shows a small graph of recorded heart rates, or you can visit the Health app on your iPhone ($1,337 at Amazon Marketplace) to view a larger, more detailed version of the graph.
Afib and EKG features
When Apple announced the Apple Watch Series 4 and its new heart rate features, the company mentioned the features would be enabled in a future update.
Specifically, the ability to alert you if an atrial fibrillation (AFib) event has been detected, along with thefeature are currently missing from the Series 4.
However, at the bottom of one of the presentation slides during the keynote, it notes that the features are coming to iOS and Series 4 in iOS 12.1 and WatchOS 5.1. Both of those updates are currently available to developers for beta testing, so it shouldn't be too long of a wait for your watch reach its full potential.
That said, there are still two features you can take advantage of on the Series 4, or for that matter, any Apple Watch that runs WatchOS 5.
High or low heart rate alerts
If you have an Apple Watch Series 1 ($269 at Walmart) or newer, WatchOS 5 is compatible and will work on your watch. The update adds a handful of new features, one of which is the ability to detect a low heart rate and bring it to your attention.
To adjust your heart rate thresholds, high or low, open the Watch app on your iPhone and select Heart Rate from the list of settings.
In the Heart Rate section, you can set the limits which will prompt the watch to alert you.
For example, if you set the High heart rate alert to 110 beats per minute (bpm), if your watch detects your heart is beating above 110bpm after you've been inactive for 10 minutes, you will receive an alert on the watch. The same can be said about the low heart rate setting -- if your heart is beating below your set threshold for 10 minutes, you will receive an alert.