Aims This study sought to determine the patient- and the therapy-related determinants of in-hospital costs for patients undergoing heart surgery at the University Hospital in Zurich. Methods and Results We performed a retrospective analysis of all adult cardiac surgical patients from the canton St. Gallen who were covered by a fixed fee arrangement (29500 Swiss francs (19470 Euro)) and referred to our institution during 1998. A total of 201 patients (143 (71%) male) with basic insurance were hospitalized in 1998 under the fixed fee arrangement. The mean age of the patients was 61·4 years (95% confidence intervals (CI): 60; 63). With the help of univariate analysis, the following pre-operative characteristics were found to be significantly associated with cost: age (PPPPPP -values P2=0·565). Conclusions These results suggest that both pre-operative (patient related) and intra-operative (therapy- and patient-related) variables are predictors of costs in cardiac surgical patients.