Heart rate variability (HRV, Heart Rate Variability) refers to the small variations in the time interval between each heartbeat. In simple terms, the heart does not beat like a metronome, with one fixed beat every second. Even if your heart rate is 60 beats per minute, the interval between two heartbeats may be 0.98 seconds, 1.03 seconds, 0.95 seconds, and so on. These variations are what we call heart rate variability. How is it measured? These variations are very small and