Many people believe that the frequency of our heart beats follows a fixed rhythm, but that is not the fact. Measurement of the electrical signals from the heart show that tiny differences occur between each heartbeat, also called heart rate variability (HRV). An average heart rate of 60 beat per minute does not mean that the interval between successive heartbeats would be exactly one second. In fact the heart beats may vary from 0.5 to 2.0 second. The interplay between the circulatory system organs and the autonomic nervous system is affected by complex biosignals (such as heart rate) which in turn contribute to a dynamic balance between the brain and the cardiovascular system. HRV is used as an indicator of the activity of the autonomic nervous system. A high HRV, which is evaluated to be associated with good cardiovascular health, indicates dominance of the parasympathetic response, the side of the autonomic nervous system that promotes relaxation, digestion, sleep, and recovery. The research literature has also established that individuals with a range of psychiatric disorders have reduced HRV, but more research in this field is needed.