[brandonb]

We'd love to do a validation study to get a definitive answer to this question.

Anecdotally, the Apple Watch is within about 5bpm of my AliveCor (an FDA-approved medical device), even while running. And it's been similarly accurate on most (but not all) patients in arrhythmias.

That said, we know accuracy will vary across skin tone, body mass index, pulse pressure, sweat, and we need to understand that more precisely before the AW can start to have real medical applications.