Apple CEO Tim Cook has often said the Apple Watch is a lifesaving device. Just recently he went on record to say he believes Apple’s longest-lasting impact on the world will be in healthcare. And today he shared a touching story from a customer that feeds neatly into his vision.

In a story posted to Twitter, Elissa Lombardo says that an Apple Watch S4 detected a problem with her husband’s heart within two days of purchase, leading to a potentially lifesaving visit to ER. The device spotted atrial fibrillation and elevated heart rates, which turned out to be symptoms of major blockages in his coronary arteries. Surgeons were able to fix him up pretty quickly and he’s now feeling much better.

It just goes to show that the kind of always-active heart monitoring the Apple Watch is capable of tracking can have some pretty serious results. These kinds of telltale symptoms can be hard to detect yourself – similar stories from other users show that elevated heart rates are sometimes wrongly attributed to anxiety and thus go without treatment for too long. Wearables can really help flag up issues like this before they become serious problems, and if Tim Cook is right, this is just the beginning.