Abstract: Objective To compare the multiple organ dysfunction score (MODS), the sequential organ failure assessment (SOFA), the acute physiology, age, and chronic health evaluation system Ⅱ(APACHE Ⅱ), the acute physiology, age, and chronic health evaluation system Ⅲ(APACHE Ⅲ) in evaluating risks for patients after cardiac surgery, in order to provide better treatment and prediction of prognosis after cardiac operation. Methods A prospective study was carried out on 1 935 cardiac postoperative patients, including 1 050 males and 885 females, enrolled in cardiac postoperative intensive care unitof Anzhen hospital between October 2007 and April 2008. The age of the patients ranged from 18 to 86 years with the mean age of 53.96 years. The patients underwent the surgery because of various cardiac diseases including coronary heart disease, valve disease, congenital heart disease, aortic aneurysm, pericardial disease, atrial fibrillation, and pulmonary embolism. We used MODS, SOFA, APACHE Ⅱ, and APACHE Ⅲ respectively to calculate the value of the first day after operation, the maximum value during the first three days, the maximum value, and the change of the value between the third day and the first day for every patient, and then we compared the calibration and discrimination of these different systems using HosmerLemeshow goodnessoffit analysis and Receiver Operating Characteristic (ROC) curve. Results There were 47 perioperative deaths because of circulating system failure, respiration failure, kidney failure, liver failure or nervous system diseases. The death rate was 2.43%. In discrimination analysis, the area under the curve (AUC) in ROC of the first day value after operation, the maximum value, the maximum value during the first three days, and the change of value between the third day and the first day for MODS were respectively 0.747, 0.901, 0.892, and 0.786; for SOFA were respectively 0.736, 0.891, 0.880, and 0.798; for APACHE Ⅱ were respectively 0.699, 0.848, 0,827, and 0.562; for APACHE Ⅲ were respectively 0.721, 0.872, 0.869, and 0.587. In calibration analysis, we compared the χ2 value of the first day value, the maximum value, the maximum value during the first 3 days, and the change of value between the third day and the first day of these systems. χ2 value of MODS was 4.712, 5.905, 5.384, and 13.215; χ2 value of SOFA was 8.673, 3.189, 3.111, and 14.225; χ2 value of APACHE Ⅱ was 15.688, 10.132, 8.061, and 42.253; χ2 value of APACHE Ⅲ was 13.608, 11.196, 19.310, and 47.576. AUC value of MODS and SOFA were all larger than those of APACHE Ⅱ and APACHE Ⅲ (Plt;0.05); AUC value of APACHE Ⅱ was smaller than that of APACHE Ⅲ (Plt;0.05). Conclusion MODS, SOFA, APACHE Ⅱ and APACHE Ⅲ are all applicable in evaluating risks for patients after cardiac surgery. However, MODS and SOFA are better than APACHE Ⅱ、APACHE Ⅲ in predicting mortality after cardiac surgery. In cardiac surgery, the complicated APACHE Ⅱ and APACHE Ⅲ systems can be replaced by MODS and SOFA systems which are simpler for use.