When we see a heart beating in a movie or on the television it usually appears as if it’s beating evenly. If we go to our doctor he may say our heart rate is 60 beats per minute or something similar. If we look a bit more closely it’s possible to see that there’s a bit more going on than first appears. If we look at each heartbeat and then compare the distance to the next heartbeat its possible to start to see that the intervals between the beats are constantly changing. Why is this? Our heart is one part of a complex system which is constantly reacting to ourselves and the world around us.One connection is to a complex series of nerves called the Autonomic Nervous System. This system, often described as the conductor, is a bit like the accelerator and brake system in a car, and one of its main roles is to detect if we are feeling frightened or feeling safe. If we are frightened the accelerator goes on and in some circumstances, we can also use the brake. If we feel safe then our system is in balance. When we detect a threat, our heart rate tends to increase so that we can either get away from or attack the threat. This tends to make our breathing rate quicker and also more shallow so that we can mobilise as much energy as possible. Our breath and our heart are closely connected. When we breathe in it tends to accelerate our heart rate, and when we breathe out it tends to slow it down. This process leads to different timings between heartbeats. It is now possible to measure the different intervals between heartbeats, and this gives us a measure called heart rate variability. This among other things gives us an understanding of how we are responding to stress. Extensive clinical research has shown a strong relationship between good heart rate variability and good long-term physical and psychological health. Poor heart rate variability is connected with poor long-term physical and psychological health. Heart rate variability has been shown to be a major influence on many experiences, such as anxiety, depression, irritable bowel syndrome, chronic fatigue syndrome, PTSD etc. Modern technology to detect heart rate variability is now easily and affordably available.