The update comes with the Apple Watch's watchOS 4, which comes out on Sept. 19.
According to Apple COO Jeff Williams, the Apple Watch's heart rate monitor is the most used in the world. Now the feature will be available to view on the Apple Watch's face, making it easier to glance at quickly, especially when working out or running. The updated feature will also show your resting heart rate and your recovery heart rate—an indicator of fitness progress.
The Apple Watch will remind you of your heart rate even when you're not thinking of it by sending notifications if you want to see when you reach a certain heart rate while working out.
The updates aren't just for personal use. Apple is also launching a new Apple Heart Study, which will track issues including heart arrhythmias.