"That can cause problems, the most common form is AFIB, it affects tens of millions of people and is a leading cause of stroke".
The Apple Watch 3 will have its usual heart rate app, but the app has been updated to monitor measurements including your resting and recovery heart rates, and to notify you if you've got an elevated heart rate when you're not being active.
To go along with this new addition, Apple announced the Apple Heart Study to look at irregular heart rhythms using data from the Apple Watch and in partnership with Stanford medicine. CNBC's Christina Farr reported that Apple is working with partners to test whether its smartwatch can be used to detect common heart conditions.
Arrhythmias, or abnormal heart rhythms, aren't always problematic. In atrial fibrillation, electrical conduction in the heart becomes disorganised.
During the event, Williams said Apple Watch can now also detect arrhythmia, an abnormal heart rhythm, and he said that Apple Watch is looking to track atrial fibrillation, a type of serious arrhythmia.
The latest edition of the Apple Watch will come with a version that includes built-in support for cellular communications, enabled via a built-in "electronic SIM", Apple COO Jeff Williams has revealed.
Greg Marcus, a cardiac electrophysiologist at UCSF who was involved with the Cardiogram study, said Apple benefits from the real-time access to raw data from its heart rate sensor.
The watches are priced from US$329 in the US. "And yes it is a business opportunity".
Apple hasn't made an official announcement about specific Apple Watch and heart related projects. Apple has not yet announced the Australian or United Kingdom prices for the device.