Apple today launched the Apple Heart Study app, a research study using Apple Watch's heart rate sensor to collect data on irregular heart rhythms and notify users who may be experiencing atrial fibrillation (AFib).

AFib, the leading cause of stroke, mey have zero symptoms, so it often goes undiagnosed.

To calculate heart rate and rhythm, Apple Watch's sensor uses green LED lights flashing hundreds of times per second and light-sensitive photodiodes to detect the amount of blood flowing through the wrist. The sensor's unique optical design gathers signals from four distinct points on the wrist, and when combined with powerful software algorithms, Apple Watch isolates heart rhythms from other noise. The Apple Heart Study app uses this technology to identify an irregular heart rhythm.

Apple is partnering with Stanford Medicine to perform the research. As part of the study, if an irregular heart rhythm is identified, participants will receive a notification on their Apple Watch and iPhone, a free consultation with a study doctor and an electrocardiogram (ECG) patch for additional monitoring. The Apple Heart Study app is available in the US App Store to customers who are 22 years or older and have an Apple Watch Series 1 or later.