Postoperative care of the cardiac surgery patient is challenging in that changes can occur rapidly. The preoperative condition of the patient as well as intraoperative events should be considered in postoperative care. Intensive care nurses are in the best position to apply knowledge into practice as they are at the patient's bedside 24 hours a day and therefore they play an important role in the post-operative care for a patient with open heart surgery in the first 24 hours. This is descriptive cross-sectional hospital-based - the study was conducted in Sudan heart Centre (SHC) with the main aim to assessment nurse's knowledge and practice for post-operative care for the patient with open heart surgery in the first 24 hours. It involved 44 ICU nurses are included in this study as from open heart surgery ICU, neurosurgery ICU, and intermediate ICU. Nurses have good knowledge for post-operative care for patient open heart surgery in the first 24 hours, but fair practice is high than knowledge. It is necessary to be aware of such measures. Without this practice, nursing knowledge and patient care are not of high standards.