Measurement of heart rate variability (HRV) in the perioperative period is not yet part of routine monitoring. Because of a lack of standardization, comparison of results of different investigations is difficult. Caution is needed in interpreting data of HRV measurements because of the complexity of autonomic control of the cardiovascular system. Moreover, confounding effects of multiple factors influencing HRV in the perioperative setting make interpretation of data difficult and limit this methodology, for example, as a depth-of-anaesthesia monitor. HRV reflects the response of the heart to a variety of influences. None of the parameters obtained, however, elucidates directly the mechanism or site of action of an anaesthetic drug. Knowledge of the pathophysiology underlying HRV is critical in order to understand the state of the autonomic nervous system and its relevance for patient management. Nevertheless, previous studies show that HRV can provide information about sympathetic and parasympathetic influences affecting the cardiovascular system in the perioperative period. Thus, HRV seems to be a useful tool for preoperative cardiovascular risk stratification. Of major concern in this context is the quality of the recording of the electrocardiogram when assessing HRV. Because of the ongoing progress in monitoring with regard to acquisition and computer-based analysis of HRV data, it seems at least possible to measure HRV routinely in the perioperative setting. However, the need for standardization requires large prospective and standardized trials. Depending on the results, the clinical relevance of HRV as a relatively simple and non-invasive perioperative monitoring has to be re-evaluated.