Starting on Thursday, the latest Apple Watch models will be able to take an ECG reading, a kind of heart-rate reading that doctors can use to diagnose heart conditions.

To activate the feature, you need the Apple Watch Series 4 and the latest version of WatchOS, which will be available for download on Thursday.

Apple made it easy to access the feature: turn on the app, hold your finger on the device’s crown for 30 seconds, and it will provide a heart rhythm reading that you can use to figure out whether you need to contact your doctor to get your heart checked out. It saves the reading in a PDF file that you can send to your doctor.