Background: Open heart surgery is a common interventional procedure for ischemic and valvular heart disease which is accompanied by postoperative care. Considering this aim of the study was framed to evaluate the effect of nursing training program regarding care of patients undergoing open heart surgery on nurses' performance. Subjects and Method:  A quasi- experimental research design was used to conduct this study. A representative sample of 30 nurses, whom dealing with open heart surgery patients were selected from the Mansoura University Hospital. Two tools were used for data collection; nurses interview sheet, and nursing practice observational Checklist. The results of the present study found that, there was a significantly improvement in nurses' knowledge and practice concerning to open heart surgery after implementation of open heart surgery nursing care training program, frequency of this improvement of nurses according to their total knowledge score at follow up phase was (73.3%) and frequency of this improvement of nurses according to their total practice score at follow up phase was (60.0%). There was a positive correlation between nurses total knowledge score and their total practices score in pre, post and follow up phases of implementing training program. Hence the study concluded that the training program had a significant positive impact on nurses' knowledge and practice concerning to open heart surgery after implementation of the training program. The study recommended: A training programs should be organized for the nurses to improve their knowledge and practice regarding open heart surgery nursing care, feedback should be done as well as booklets about open heart surgery should be available in cardiothorathic department in the hospital