Background: Cardiopulmonary bypass machine is a machine that takes over the function of the heart and lungs during open heart surgeries. It incorporates an extracorporeal circuit to provide physiological support with safety precautions to deliver optimum patient care. Aim of the study: To assess intraoperative nursing safety precautions for open heart surgery patients on cardiopulmonary bypass machine in cardiac surgery unit. Research design: Descriptive research design was adopted to conduct this study. This study was conducted in cardiac surgery unit, Heart Hospital of Assuit University. Subjects A convenient sample of 60 adult male and female patients who presented for undergoing cardiac surgery using cardiopulmonary bypass machine in addition to 20 critical care nurses acts as a perfusionist and willing to participate in the study. Tools: Patient assessment sheet and nursing safety precaution assessment sheet was used. Results: Most of nurses (90%) had satisfactory performance for patient safety, while Assessment of possible complications during cardiopulmonary bypass machine, founded that off 21 studied complications Arrhythmias is the commonest complication present in 11of studied patients.in cardiac surgery unit. Conclusion: Critical care nurses in cardiac surgery unit had satisfactory performance for patient safety. Recommendations: Perfusion safety and communication with the whole team must be at the highest level. In line with this information, the use of these systems can become standard in cardiac surgery.