Part of the watchOS 5.2 update, the ECG app can capture heart rhythm in a moment when users experience symptoms such as a rapid or skipped heart beat.
The number comes from a massive RAND Corporation study which included 400,000 participants across the US, Europe and South Africa.
Announced as one of key features of Apple Watch Series 4, the ECG functionality will be released by the end of the year as part of the next software update.
Clinical study utilizes the Zimmer Biomet mymobility app on Apple Watch and iPhone to guide patients through pre- and post-op care.
The new wearable further cements the iPhone maker's dominance in the smart wearables space.
Researchers used data from 14,000 Apple Watch users and was able to detect that 462 of them had diabetes by using the Watch's heart rate sensor.
The ResearchKit-based study launches in partnership with Stanford to identify irregular heart rhythms.
The company has also introduced the SmartRhythm feature that continuously monitors heart rate from the Apple Watch.
The iPhone maker has also announced the Apple Heart Study to identify irregular heart rates, including potentially serious heart conditions such as Afib.
The insurer, which covers 23 million, is already offering Apple's smartwatch to its 50,000 employees as part of its corporate wellness program.