The SelfLoops HRV application calculates and displays the heart rate variability. This application is used by pro athletes and olympians. Heart rate variability (HRV) is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat (called R-R) intervals. There are several metrics used in the scientific literature, we calculate: SDNN, RMSSD, pNN50, AVNN. We also calculate the same metric used by BioForce HRV and ithlete,