Apple has designed a new algorithm that Apple Watch uses to measure electrocardiogram (ECG) waves, according to developer documentation for the iOS 14.3 and watchOS 7.2 betas.
In the official documentation, a new "version 2 algorithm" declaration has been added. No other information is included.
The ECG feature includes irregular heart rhythm detection, which intermittently measures the user's heart rate in the background and sends a notification if it detects an anomaly it categorizes as atrial fibrillation, which can be a serious heart arrhythmia condition.
Based on beta code uncovered by MacRumors, it's likely that the new algorithm will allow the ECG app to check for atrial fibrillation (AFib) at higher heart rates - during exercise, for example.
iOS 14.3 will introduce support for Apple Fitness+, Apple's upcoming fitness service that will work with the Apple Watch, plus it brings a new Cardio Fitness feature that lets you know if your VO2Max levels are low. VO2Max is a useful measurement of overall fitness and heart health.
iOS 14.3 is set to be released on Monday, December 14, which is also the day that Apple Fitness+ is coming out.
Wednesday October 7, 2026 12:02 pm PDT by Juli Clover
Some Apple Watch Series 12 and Ultra 4 owners have experienced unexpected skin irritation with the new models, according to reports on the MacRumors forums and Reddit.
Affected users complain of a burning sensation and redness under the sensor area. The Apple Watch Series 12 and Ultra 4 measure heart rate every five seconds, and some people have wondered if that's the cause of the skin...
Friday October 9, 2026 10:20 am PDT by Juli Clover
For this week's giveaway, we've teamed up with Southern Straps to offer MacRumors readers a chance to win an Apple Watch Series 12 and a nylon band from Southern Straps to go along with it.
Southern Straps is a California-based company that has been making high-quality bands for the Apple Watch since the device first launched in 2015, and the company's selection of bands offer a an...
Tuesday October 6, 2026 6:09 am PDT by Tim Hardwick
Apple's $634 million patent loss to medical technology company Masimo has just gotten even bigger, after a federal judge ordered Apple to pay an additional $184 million in interest on what it owes (via Bloomberg Law).
The ruling takes Apple's bill to around $818 million, but that doesn't include any post-judgment interest continuing to accrue until the judgment is paid.
Judge James Selna ...
Wait what? The ECG only works when your finger is on the Digital Crown. It can’t work in the background.
The background irregular heart rhythm detection does not use the ECG but it is grouped with the ECG features (which is technically inaccurate but they are related features, just different technologies). It's been around as long as the ECG: "Using the optical heart sensor in Apple Watch Series 1 or later, the irregular rhythm notification feature will occasionally check the user’s heart rhythm in the background for signs of an irregular heart rhythm that appears to be AFib and alerts the user with a notification if an irregular rhythm is detected on five rhythm checks over a minimum of 65 minutes." (https://www.apple.com/newsroom/2018/12/ecg-app-and-irregular-heart-rhythm-notification-available-today-on-apple-watch/)
Still waiting for ECG in Japan! Any news about it?
Since ECG received final medical approval in Japan this September, I guess maybe iOS 14.3 will cover ECG functionality also Japan as well? *finger-crossed*
