The New England Journal of Medicine recently published a study that followed the ability of an Apple Watch to detect heart abnormalities. The most common form of irregular heartbeats is atrial fibrillation, which can increase the risk of a stroke. Many of those who have this issue are unaware, leading to the Apple Watch possibly uncovering issues before they cause problems. 2,161 subjects in the study had a detected irregular heartbeat from the smartwatch, and 71% of them were found to truly have atrial fibrillation.
Source: https://www.forbes.com