The nursing care should be guided by clearly defined standards to ensure the high quality of care. Standards of care are definitive statements that describe a common or acceptable level of patients care or performance.The aim of this study is to evaluate the effect of nursing care standards on nurses'performance regarding caring for patients with cardiac arrhythmias in CCU at Benha university hospital. Research hypothesis are:the mean score of nurses' knowledge and practices level post NCSs implementation may be higher than their score pre NCSs.A quasi-experimental research design was utilized to conduct the aim of this study.This study was conducted in coronary care unit (CCU) at Benha University Hospital.Sample: All available nurses working in CCU at the time of study were included in the study. Two data collection tools were used in the different phases of this study: First tool:Self-administered questionnaire sheet for nurses to assess nurses’ knowledge. Second tool: Nurses' practice observational checklist based on the designed NCSs.The results of the study showed that statistical significant improvement in the total mean knowledge scores of nurses in all items of the study post implementing the standards(P= 0.000) as compared to pre implementing period. Also there was statistical significant improvement in the total mean practices scores of nurses in all items of the study post implementing NCSs (P= 0.000).Conclusion: there is a statistically significant improvement in nurses' performance regarding caring of patients with cardiac arrhythmiasin CCU post NCSs implementation.The study recommendedNCSsfor management of patient with cardiac arrhythmias should be revised,updated and available in CCU in both Arabic and English language. _____________________________________________________________________ Key Words:Nursing care standards, Cardiac arrhythmia, Nurses'performance