https://techcrunch.com/2017/09/12/apples-watch-3-rolls-out-heart-health-and-smart-fitness-features/

Today, Apple announced the new Apple Watch 3 will be rolling out several health and fitness features included with OS4 like smart activity coaching, new features for swimmers, Gym Connect and an enhanced heart rate monitor.

Apple will enhance the heart rate app to monitor measurements like resting heart rate, recovery heart rate as well as a notification for an elevated heart rate when you don’t appear to be active. The other interesting thing to note is the tracking of heart rhythm. This is particularly helpful for those with an irregular heart beat or who may not know they have one.