Background:  Cardiac arrhythmias are the most prominent causes of mortality in patients with heart diseases. The critical care nurse role in cardiac arrhythmia mainly focuses on, prevention, early detection and taking emergency actions. Aim: to evaluate the effect of an educational program regarding cardiac arrhythmias on nurses' knowledge in critical care units. Subjects and method:Design: A quasi-experimental design was applied. Setting: The study was conducted at Critical Care Units in Governmental Port-Said general hospitals (Port Said general hospital, Pour -Fouad general hospital and Alzhoor central hospital) recently universal health insurance hospitals in Port Said. Subjects: Convenient sample of all available nurses 139 nurses in critical care units divided into 116 female and 23 male, who attended the research setting and were included in this study. Tools: Tool: Self- administered questionnaire to assess nurses knowledge regarding cardiac arrhthmais, which includes part I: Demographic characteristics, part-II: Self- administered questionnaire of nurses regarding cardiac arrhthmais. Results: showed that more than three quadrants of the studied nurses were female aged less than thirty years old and slightly more than half of them holding diplome degree in nursing. The studied sample demonstrated a significantly higher level of knowledge (P 0.001), with a high reported satisfactory knowledge level 77%) in post-intervention than the pre-intervention (13.7%). Conclusion: Improvement of a nurses knowledge about cardiac arrythmais after the implementation of the education program. Recommendations: Continuous education programs for nurses in different critical care settings are highly recommended.