https://techcrunch.com/2022/06/06/watchos-9-adds-new-modes-and-watch-faces/

During a keynote at Apple’s Worldwide Developers Conference, the company debuted the latest version of watchOS, the operating system that runs on the Apple Watch.

Apple claims that it has improved the Apple Watch’s ability to detect arterial fibrillation (A-fib), an irregular heartbeat that can lead to blood clots, stroke, heart failure and other heart-related complications. With the arrival of watchOS 9, supported Apple Watch device models can now detect “burden,” or how often a person experiences A-fib over a certain amount of time.