This app uses the camera to measure your heart rate and calculates your heart rate variability.

HRV is an index of activity of the autonomic (vegetative) nervous system.

The higher your HRV, the higher the balloon will fly (biofeedback).

Focus on your vivid heart (and calm breathing) and get an idea what helps you calming down (what makes the balloon rise).

The measurement quality highly depends on correct usage (your finger should be placed in a way that the camera can clearly see your blood flow and you should limit the movement of the measured finger as good as you can).

Measuring the HRV right after physical activity is not the purpose, as the HRV has a different meaning for higher heart rates.

The area around the camera will get warm during measurements. That's normal.

Heart rate variability (HRV) is calculated the following way:
Imaging of bloodflow in your finger is used to create a photoplethysmogram (PPG). With the PPG it then calculates the interbeat interval (IBI), resulting in your heart rate (BPM), and - through filtering of artifacts and more calculations - the 'root mean square of successive differences' (RMSSD). While the HRV itself is not clearly defined as one unit and can be calculated in different ways, the RMSSD is the most common method.

Disclaimer:
This is not a medical app!
If you have any medical problems, please consult a medical practitioner and don't make any decisions based on the measurements of this app.