Changes in cardiovascular reactivity have been used as a psychophysiological marker of various emotional states in both children and adults. Recent decades have seen increasing use of heart rate variability as a non-invasive marker of cardiac autonomic function and of central processes involved in autonomic function regulation. Developmental research has linked cardiac vagal tone to an individual's responsivity to environmental challenges and a decrease in vagal component of heart rate variability may reflect deficiencies in emotional regulatory system. Studies with children and adolescents suggest that attenuated cardiac vagal function is seen in various pathophysiological conditions characterised by emotional dysregulation. Thus, alteration in cardiac vagal modulation may be the common mechanism underpinning the association between negative affective states, emotional dysregulation and risk for cardiac disease.