Elite HRV is in my opinion one of the best HRV apps out there - and it works with a lot of chest straps etc. It would be great to have an alternative to the quite expensive Oura ring for HRV data. Elite HRV recently asked for suggestions for integrations so I think they’re very open for working together.

Not possible as no API, but if they sync the data to Apple Health and/or Google Fit, a direct integration wouldn’t be necessary.