Effect of Various Lengths of Respiration on Heart Rate Variability during Simple Bhramari (Humming) Heart rate variability (HRV) is a physiological phenomenon that measures the variation in time between successive heartbeats. High HRV is associated with a healthy and flexible autonomic nervous system, reflecting the body's ability to adapt to different situations. It is often seen in individuals with good cardiovascular health and resilience to stress. On the other hand, low HRV may indicate a less adaptive autonomic nervous system and can be associated with various health issues, such as cardiovascular disease, chronic stress, or other conditions affecting autonomic function.