- Power spectrum analysis of heart rate variability (PSA of HRV) is a promising method, which can be used as an index of cardiac autonomic balance. PSA of HRV is a noninvasive technique, based on ECG sampling of RR interval variation, thus providing a dynamic assessment of sympathetic and parasympathetic tone, reflecting the interactions between the two. It has been shown to have potential value in various laboratory and clinical conditions. It is influenced by many factors such as age, sex, position, breathing, smoking, hour of the day and medications. Different methods of data processing by various authors have often elicited conflicting results. Standard values are not yet available to be used or compared in different settings. From the interest it has raised, it may be expected that this method will be in widespread use in clinical practice in the future, providing a useful tool, both for diagnostic and prognostic purposes, as well as serving as a further aid towards monitoring therapeutic interventions. This review highlights techniques of dynamic assessment of HRV and studies of its clinical applications in psychiatry in particular. It raises the potentially important prognostic implications of protracted autonomic dysfunction in psychiatric patient populations, especially for cardiovascular morbidity and mortality.