Background: Cardiac surgery places children at risk for numerous significant health problems and complications. Children with surgical procedures require an earlier intervention to improve outcome. Systematic nursing intervention is vital during the post-operative period to identify rapidly any complication and deterioration in children condition. Aim of this study was to assess the pediatric nurses' performance regarding postoperative care of children with cardiac surgery. Design: A descriptive study design was used. Setting: The study was carried out at the Pediatric Intensive Care Units for postoperative heart surgery in Cardiac Surgery Academy. Subject: A purposive sample composed of 60 nurses working at the previously mentioned setting and giving care for children with cardiac surgery. Tools: It included two tools; a predesigned interviewing questionnaire and observation checklists. Results: Half of studied nurses their age ranged from 25 to 30 years and more than half of them had 5 to 10 years of experience. Less than one quarter of the studied nurses had satisfactory total knowledge while less than half of them had competent practices regarding care of children with cardiac surgery. There was a significant correlation between total knowledge and total practices of studied nurses (P value < 0.05). Conclusion: It can be concluded that, slightly more than one third of the studied nurses had competent level of performance regarding postoperative care for children undergoing cardiac surgery. Recommendations: Continuous educational training programs should be organized for the nurses especially newly joined nurses to improve their knowledge and practice regarding cardiac surgery.