The Acute Physiology and Chronic Health Evaluation (APACHE) score was developed to assess disease severity. Once organ failure develops, laboratory values and hemodynamic parameters should be monitored to assess the degree of impairment. This study aimed to assess nurses’ performance regarding using the APACHE scoring system and its effect on the outcomes of patients with cardiac surgery. A quasi-experimental research design (one group pretest and post-test) was used to achieve the aim of this study. The convenience sample consisted of all available nurses (n=50) working in intensive care units of cardiac surgery at Ain Shams Specialized Hospital and in the Cardiovascular and Thoracic Academy affiliated with Ain Shams University hospitals. Additionally, a purposive sample of 130 patients with cardiac surgery was included in this study. Data was collected using nurses’ self-administered questionnaires, observation checklists for nurses, attitude scales of nurses, patient assessment questionnaires, and nursing-sensitive patient outcomes measuring scales. The findings showed a highly statistically significant difference between the mean score of total nurses’ level of knowledge, practice, and attitude before and after the educational program. Also, a highly statistically significant difference was observed in the total score of patient outcomes before and after the implementation of the educational program. Implementing an educational program positively affected nurses’ performance; the APACHE score has an efficient and comparable discriminative ability to predict the outcomes of patients undergoing cardiac surgery. The study recommends conducting periodic training programs for nurses in cardiac surgery intensive care units to equip them with the latest knowledge and skills in using the APACHE scoring system to predict patient outcomes and complications within the first 24 hours.