> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/faq/help-topics/data-api-sdk/provider-coverage-and-per-provider-data-availability/apple-bpm-minus-one-source-data.md).

# Why is bpm -1 in Apple heart rate samples?

A `bpm` value of `-1` typically **originates from the source data in Apple Health**, not from Terra processing. Terra forwards what the health source provides.

To check, **open the Apple Health app's 'all data' view for those timestamps**. A third-party app may be writing `-1` directly into HealthKit.