The interaction between increased Intra Abdominal Pressure (IAP) and Intrathoracic Pressure under different Positive End Expiratory Pressure (PEEP) levels is intriguing, since these two conditions coexist frequently in several clinical settings. The aim of our study was to investigate the interaction between different PEEP levels and increased IAP during laparoscopic cholecystectomy. In fifty two patients, who underwent scheduled laparoscopic cholecystectomy, cardiovascular parameters were determined by an Oesophageal Doppler Monitor device during two different time periods, before and after pneumoperitoneum, and under five conditions: (i) PEEP 0 cmH₂O (ii) PEEP 5cm H₂O (iii) PEEP 10cm H₂O (iv) PEEP 15cm H₂O and (v) in the absence of PEEP or ventilation. Cardiac output and stroke volume showed a statistically significant decrease compared to the baseline value after the application of different PEEP levels, when there was no pneumoperitoneum (p<0.05). However, both parameters increased, when PEEP and pneumoperitoneum were applied together (p<0.001). Corrected flow time, peak flow velocity in the descending thoracic aorta and mean acceleration showed similar alterations but not at all PEEP levels. Finally, αt the no PEEP or ventilation phase, the negative effects of increased IAP on the cardiocirculatory function were predominant. According to these results, application of PEEP seems to counterbalance the negative hemodynamic effects of increased IAP. Moreover, it could also be concluded that ‘ideal’ PEEP level might be the one that borders the IAP level, since the best cardiac output and stroke volume values were reported at that point.