Scary? For sure. According to the Centers for Disease Control (CDC), an estimated 2.7 to 6.1 million people in the United States have AFib , but only 2% of people younger than age 65 have AFib. Someone who experiences AFib and wears an Apple Watch (with the irregular heartbeat notifications turned on) could theoretically detect when they're in AFib, and then take that data to their doctors. "This is just meant to be a way to capture that information in that moment, so that you can go in and have a conversation with a doctor to understand what was going on," Dr. Desai says. "We don’t want people to diagnose off of it. We don’t think it’s the full picture of your heart, it's just a subset of what's going on in your heart."