We’ve regularly heard stories of the Apple Watch’s health features helping save a user’s life. Now, another such story has popped up on Reddit, with an Apple Watch Series 4 user explaining how the device’s ECG app alerted him to bigger problems.

Phil Harrison writes that he was training for the Brighton Marathon when he started experiencing heart palpitations that wouldn’t stop. He then used the ECG app on his Apple Watch to see what was wrong. Of note, Harrison says the ECG app had only been available in the UK for a week when he used it:

The Apple Watch’s ECG result prompted Harrison to seek medical attention, a process that ultimately led to him needing open heart surgery:

More than anything, this story underscores the impact of Apple’s continued expansion of the ECG functionality around the world. When the ECG app on Apple Watch was originally released, it was limited to the United States. Since then, however, the functionality has gradually expanded to more countries. View the full list here.

Read more stories of Apple Watch helping save people’s lives in our full Apple Health guide.