Postoperative complications assessment in pediatric cardiac surgery have been importantly to reduce mortality, hospital stay, cost, and quality of life after pediatric cardiac surgery. Aim: To assess postoperative complications among children with open heart surgery. Design: A descriptive exploratory design. Settings: The study carried out in cardiology unit and open heart intensive care unit at specialized Cairo- University pediatric hospital. Subjects: A purposive sample composed of sixty children after open heart surgery and less than 5 years of age. Tools of data collection: Structured questionnaire sheet and observational checklists for cardiac and extra cardiac complications assessment. Results: More than two fifths of the children were infants, less than two thirds of them were males, less than three quarters had consanguinity, the most common type of cyanotic and acyanotic defects were TOF and coarctation of the aorta respectively, the vast majority of children had postoperative complications either psychological or physical; more than one third of children had pain, regarding psychological complications less than one third had anxiety, regarding physical complications; near one third had sternal wound infection, less than one quarter had pneumonia, the minority of children had vomiting and diarrhea, less than one fifth of children had arrhythmia, the minority of children had developed acute renal failure, peritoneal dialysis, hyperglycemia and bleeding after operation. Conclusion: The most present complications was pain followed by anxiety and fear, sternal wound infection, pneumonia, vomiting and arrhythmia. The factor associated with postoperative complications were cyanotic heart defect, infant stage, underweight and lenghth of stay one month and more in hospital. Recommendation: Regular assessment and monitoring of children after open heart surgery to detect any complications early to be managed immediately. Special attention should be given for younger children with heart cyanotic defect, underweight, and had long stay in hospital.