Apple and Johnson & Johnson announced a new study called Heartline to find out if the Apple Watch can help reduce the risk of stroke and detect atrial fibrillation (AFib) early.

Although AFib is the leading cause of stroke, Johnson & Johnson said it can be hard to diagnose because people often don’t exhibit symptoms. For what it matters, Apple already offers AFib detection on the Apple Watch Series 4, but that capability obviously needs some additional work — or at very least, it needs to be tested in real-life situations.

“The Heartline Study is a nationwide, randomized, controlled, app-based, virtual research study sponsored by Janssen Pharmaceuticals, Inc., a member of the Janssen Pharmaceutical Companies of Johnson & Johnson,” the companies said. “The team worked with Apple to jointly design the research study and the Heartline Study app.”

The enrollment for the new study has officially begun, and it’s open to anyone 65 or older with traditional Medicare and an iPhone 6s or later model running iOS 12.2 or newer.

“Eligible participants will be randomized to one of two possible groups. One group will participate by only using the Heartline Study app on their iPhone,” Johnson & Johnson explained. “The other group will participate by using the study app on their iPhone in addition to obtaining an Apple Watch to use the ECG app and irregular rhythm notification feature. Participants who already own an Apple Watch may be eligible to join the study as well, with certain restrictions.”

Participants selected in the Apple Watch group can either purchase a watch at a discounted (though not disclosed) price or can borrow a watch on loan for no cost.

The Heartline study app is available for free in the iTunes App Store.

The study will last three years and includes two years of active engagement and one year of additional data collection.