Send your Heart Rate to the Health app from your Bluetooth LE Heart Rate Monitor. In addition to seeing your heart rate in-app, the app will continue to run in the background, adding your heart rate to the Health app once a minute.

You can also easily export a CSV of your heart rate over time.

This app has no ads, and doesn't sell (or even track) your usage to anyone, ever.

Note that Fitbit devices won't work with this app, due to them locking down their Bluetooth communications.