The influence of the heart and circulatory system occurs within milliseconds, and every single heartbeat plays a role. The role of the heart in the psyche and cognition is evident in the high coincidence of cardiovascular diseases, such as high blood pressure and heart attack, and mental illnesses, such as depression and anxiety disorders.
There are a number of explanations for this high coincidence, but none of them have been definitively proven yet. For example, negative psychological reactions to a diagnosis of cardiovascular disease are cited as a reason for the development of mental illness. On the other hand, an unhealthy lifestyle in the presence of mental illness is considered a risk factor for the development of cardiovascular disease.
The concept is based on integrated brain–body states. Every physical process, such as a heartbeat or any change in blood pressure or metabolism, is automatically accompanied by a mental or psychological process. This means that the two are inextricably linked.