Based upon the hypothesis that prognosis in childhood heart failure depends on autonomic dysfunction, the author introduced a new heart failure model and a medical therapy with beta-blockers in 1996. The author used the analysis of heart rate variability (HRV) in 24 hours Holter ECGs for the understanding of the pathophysiology of childhood heart failure and for objective control of medical therapy. The success of this clinical model was the inspiration of a new approach to mental disease in childhood. In the last decades, an increase of new paediatric problems requiring medical care like eating disorders, behavioural and attention problems has been observed. All these diseases are related to autonomic dysfunction and have a high impact on cardiovascular prognosis. Based upon the hypothesis that behavioural problems are accompanied by changes in the autonomic nervous system, the author performed analysis of HRV in 24 hours Holter ECG's in these patient groups: healthy children with respect to school affiliation; a historical control group from literature published in 1997; attention deficit disorder with and without hyperactivity; anorexia nervosa and obesity. This data was compared to children with an increased cardiovascular risk due to congenital heart disease. In order to analyse the effect of autonomic function on human growth, we measured HRV in children with growth failure. A new HRV Score was established for the comparison of autonomic function in different age groups. The author could demonstrate a decrease of vagal activity in healthy children in children of today and speculate that insufficient vagal maturation may be a reason for an increasing prevalence of mental and cardiovascular disease. Looking for the reason of this vagal shift, caloric over nutrition, omega-3-fatty acid deficiency, high intensity of information and communication technology usage and some environmental toxins reduce HRV in childhood.