Amazing story shared by Scott Killian with 9to5Mac:

Then Killian, who wears his Apple Watch to bed three to four nights a week for sleep tracking, says his Apple Watch woke him up around 1 am with an alert from a third-party app called HeartWatch saying his resting heart rate was elevated while sleeping (Apple recently introduced a built-in feature that can do this with Apple Watch Series 1 and later). Killian experienced mild indigestion which can be a sign of a heart attack, but says he generally didn’t feel sick.

His Apple Watch charted his heart rate at around 121 beats per minute in the middle of the night while data previously captured showed his average resting heart rate at around 49 beats per minute. The data also showed that this was the first time his resting heart rate had reached this level since he began wearing Apple Watch, so he decided to go to the emergency room as a precaution.

I’ve been using HeartWatch since it came out in late 2015 – if you care about heart rate stats monitored by the Apple Watch, I can’t recommend it enough.