The Apple Watch's built-in heart rate monitoring has helped a user in calling ER at the right time when the smartwatch indicated that his heart rate had suddenly become abnormal. Although the user passed out en route to the hospital and was later diagnosed with SVT, timely alerts from the Apple Watch has ensured prompt response from ER without delay thus, saving his life.
https://www.notebookcheck.net/Apple-Watch-s-heart-rate-monitor-saves-a-man-s-life.415928.0.html