BACKGROUND: Major scores for the evaluation of procedural risk in cardiac surgery are the European system for cardiac operative risk evaluation score (EuroSCORE), the Society of Thoracic Surgeons (STS) score, and the Parsonnet score. The aim of our study was to analyze the predictive value of these scores in "high risk" patients undergoing isolated aortic valve replacement (AVR).METHODS: Six hundred and fifty-two patients underwent isolated AVR from January 1999 through June 2007. Emergency and redo operations were included; acute endocarditis was excluded. Evaluation was performed by logistic regression analysis. Data collection was prospective.RESULTS: The mean logistic EuroSCORE of all patients was 8.5 +/- 7.9%, the mean STS score was 4.4 +/- 3.9%, and the mean logistic Parsonnet score was 9.8 +/- 8.5%. In-hospital mortality was 2.5% (n = 16). Freedom from all-cause death was 93.4% at 1 year, 90.2% at 2 years, and 75.8% at 5 years, respectively. A total of 182 patients had a logistic EuroSCORE greater than 10. For the group of patients with a EuroSCORE between 10% and 20% (n = 130) the mean EuroSCORE was 13.9 +/- 2.8% and the STS score was 6.5 +/- 3.8%. Observed mortality was 4.6% in this group. For the 52 patients with a logistic EuroSCORE of at least 20 (mean 28.5 +/- 10.3%, STS score 10.1 +/- 7.3%) the observed mortality was 3.9% (n = 2). By stepwise logistic regression, none of the EuroSCORE variables could be identified as an independent predictor in the "high- risk" group.CONCLUSIONS: The logistic EuroSCORE was primarily created to allow patient grouping for the total spectrum of cardiac surgery. In patients undergoing isolated AVR, the EuroSCORE highly overestimates mortality, whereas the STS score seems to be actually more suitable in assessing perioperative mortality for these patients.