The ECG app on the Apple Watch Series 4 is getting a lot of positive reviews, along with some skepticism about its ability to accurately detect atrial fibrillation (AFib) in adults under the age of 55.

Some say it even helped save their lives, while most are not even sure how to take an ECG with the new app.

Apple shows you how to take the ECG Test. Click on the image below to open a larger version in a new browser tab.

How to use ECG app to take an ECG Test on Apple Watch Series 4

We also found a great video to show you how it’s done.