Abstract
One of the markers of the functioning of the autonomic nervous system is the heart rate variability. It has been used in research and clinical practice as a noninvasive method to determine its activity. Its measurement is made by setting statistical parameters of the variation that exist beat to beat in the electrocardiogram, which can be characterized in time and frequency domains. The time domain is the most basic description of this variability and allows obtaining the frequency domain. In the latter, a high frequency component is measured, which is related with the respiratory sinus arrhythmia and the behavior of the parasympathetic branch. The low frequency component has a controversial interpretation and may represent the combined effect between the sympathetic and parasympathetic branches, modulated by the baroreflex. Neural control of the heart rate variability involves the encephalic system, the spinal cord and local systems, which are influenced by afferences of mechanoreceptors, chemoreceptors and baroreceptors. Applications of the analysis of the heart rate variability are still discussed and involve a wide variety of fields such as exercise, cardiovascular diseases and their risk factors, as well as psychopathologies.