Janssen Pharmaceutical Companies, a Johnson & Johnson subsidiary, is partnering with Apple to study atrial fibrillation (AFib) and how wearable technologies, like the Apple Watch, can help people identify AFib and treat it before a health crisis occurs.

AFib is an irregular heartbeat rhythm and the leading cause of stroke in the U.S. According to Janssen, up to six million Americans have AFib and, because the condition often has no symptoms, patients may not learn of it until they suffer a serious cardiac event, like a stroke or heart attack.

Janssen’s partnership with Apple, called the Heartline study, is aimed at detecting those unidentified AFib cases. It’ll also help researchers determine whether technology can be used to predict cardiac events before they occur, and also allow them to study heart health outside of a clinical environment with real-world information.

The Heartline study will only be available to patients 65 years or older, who are both U.S. residents, and have Original Medicare coverage. Study participants in the study must also own an iPhone 6s or later and agree to hand over their Medicare claims data to researchers.

One group of participants will only use a Heartline Study app on their iPhone or Apple Watch that provides regular educational notifications, tips, surveys about heart health and generally improving the organ’s functioning.

Another group of participants will need to wear their own Apple Watch during the study. The Apple Watch will continually transmit the study participants’ heart rhythms to the Heartline Study app, which will identify any suspected AFib rhythms and notify users when that happens.

The study will take place over three years, including two years of “active engagement” with notifications and other educational content transmitted to every participant, as well as an additional year of data collection. Researchers will then evaluate the data to see if wearing an Apple Watch and understanding heart health can lower the incidence of cardiac events.

Apple’s partnership with Johnson & Johnson is part of a broader healthcare push by Apple. Last year, Apple released the results of a heart study it conducted with Stanford University, and in September, announced a new Research app for researchers to collect and share user data, along with studies about heart health, women’s health, and hearing.

Apple CEO Tim Cook has also talked extensively about the role Apple and Apple Watch could play in improving health outcomes. Last year at the Time 100 Summit in New York, Cook said Apple may ultimately be remembered as a healthcare company.

“I do think there will be the day that we will look back and say that Apple’s greatest contribution to mankind was in health care,” Cook said.

People interested in participating in the Heartline study can sign up here.

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