Awesome
HeartBeat
<img src="https://fdroid.gitlab.io/artwork/badge/get-it-on.png" alt="Get it on F-Droid" height="80">
A very simple heart rate monitor for Android.
To initiate a measurement, start the app and place your finger on the camera, covering the flash as well, and keep still. The measurement takes roughly 10-15 seconds.
Once it is complete, the results, and the raw data is shown. While the app doesn't keep a log, these results can be copied.