Background:The assessment of the risk of death and the estimated length of stay in the intensive care unit is a relevant clinical practice to predict the severity of the disease and to outline effective strategies for patient improvement and hospital quality indicators. Aim: This study aimed to assess nurses' performance regarding using of APACHE scoring system. Research design: Descriptive exploratory research design was utilized to achieve the aim of this study. Subjects: A convenience sample of all available nurses (50) working in the cardiac surgery intensive care units at Ain Shams Specialized Hospital, as well in the Cardiovascular and Thoracic Academy affiliated to Ain shams university hospitals. Tools: (1) Nurses' knowledge assessment questionnaire. (2) Nurses' observation checklist. (3) nurses' attitude scale. Results: The majority of the cardiac surgery ICU nurses had inadequate knowledge, practice and attitude regarding using of APACHE scoring system. Conclusion: Cardiac surgery ICU nurses had unsatisfactory performance (knowledge, practice and attitude) regarding using of APACHE score. Recommendations: Conducting periodic training program for cardiac surgery intensive care units' nurses in order to keep them with the updated knowledge, practice and attitude regarding using of APACHE scoring system to predict complications among patients with cardiac surgery during the first 24 hours.