The newest update for Apple Watches is out now, bringing a highly anticipated feature to Series 4 devices. Apple pushed out watchOS 5.1.2 today, which includes its ECG app for monitoring irregular heartbeats.

Apple Watch Series 4 devices all have built-in electrodes that can measure electrocardiograms, or ECGs. At the time of the Watch’s debut in September, Apple’s native app with which the electrodes communicate wasn’t ready for consumer use. Now, it’s rolling out as part of the watchOS 5.1.2 update.

The ECG app is for the Watch itself, while ECG data gets stored in Apple’s Health app on iOS devices. To take an ECG reading, users must place their finger on the flat side of the Digital Crown on their Series 4 Watch. The electrode on the Digital Crown communicates with the other electrode on the Watch, which sits near the heart rate monitor, to take a complete ECG measurement.