Heart rate variability (HRV) analysis has gained a large interest as a method for the assessement of the autonomic nervous function. Standards of measurement of HRV, constituted in 1996, has enabled to systematize methods being used for the analysis. Time domain analysis of HRV provides mainly quantitative data. Frequency domain gives possibility to quantify the variance at each specific frequency: HF (high frequency - around 0,02 Hz), LF (low frequency - around 0,01 Hz) and VLF (very low frequency - around 0,003 Hz). HF component is recognized as a marker of the parasympathetic activity. LF component is influenced both by vagal and sympathetic activities. Physiologic components of VLF have not been fully explored. The role of the autonomic nervous function in human hypertension has been widely investigated. In early phases of hypertension sympathetic predominance has been found, mediated both by increased sympathetic stimulation and a decreased parasympathetic tone. As a disease advances, sympathetic overactivity is Less evident, evolving into established high resistance hypertension. However, this should not be viewed as a normalization, since sympathetic tone in relationship to vascular hyperresponsiveness remains excessive. Heart rate variability as the method of assessement ofthe autonomic nervous function enables insight in to patophysiology of human hypertension and is widely used in experimental and clinical studies.