Recent research demonstrates that about a third of all postoperative complications are due to cardiovascular reasons, and in addition, more than every second postoperative death is attributed to major cardiovascular events. Increasing evidence indicates that the compromised autonomic nervous system (ANS) shows a strong correlation with adverse cardiovascular events. With the intention to reduce perioperative risk for patients, assessment of ANS activity might be used as a risk indicator. It has been proposed that - additionally to other factors mechanical positive pressure ventilation may cause stress to the ANS. A possible method to observe the ANS activity is heart rate variability (HRV) analysis. In this study, we investigate the influence of two ventilation modes on HRV. To be more specific, we apply classical pressure support ventilation with positive endexpiratory pressure levels and the novel variable pressure supported ventilation (VPS), which varies the pressure support with each breath in a pre-set range. The 15 included patients were ventilated for 1 hour both ways and the resulting parameters of HRV and clinical parameters, such as blood oxygen saturation, blood pH level and other physiological parameters, were assessed and compared. Results show no significant differences of HRV parameters between both groups. Also the variability of applied tidal volumes is not influenced significantly by the VPS. Concluding it can be said, that with this study we were not able to detect any relevant advantage of VPS regarding heart rate variability and further research will be necessary to show any significances. This may be started with another clinical trial, which only investigates the impact of variable pressure support on applied tidal volumes, which could be performed in study design, which is easier to perform.