Monitoring of cardiac output (with subsequent haemodynamic optimisation) may improve outcome after high-risk surgery. The pulmonary artery catheter is still considered the gold standard, but has potential serious complications. Much effort has been put into developing equally good, but less invasive techniques. One of these, the LiDCOplus™ system, uses pulse power analysis to calculate cardiac output and is calibrated by a lithium indicator dilution technique. Since cardiac output is affected by the compliance of the aorta, the LiDCO calculates a calibration factor (CF) each time it is calibrated. The purpose of this study was to investigate whether insertion of aortic prosthetic material would affect aortic compliance and thereby the CF. It was hypothesised that the change in CF would be larger in patients with aortic occlusive disease (AOD) than in patients with aortic aneurysm disease (AAD), since previous studies have shown that these two groups differ considerably on both haemodynamic capacity and their response to aortic cross-clamping [1].