Background: Cardiac arrhythmia can cause more fatal forms of rhythm disturbance. Nurse in critical care units plays a necessary role in arrhythmias management specializes in symptomatic relief, promotion of comfort and taking crisis intervention in fatal forms of dysrhythmias. Aim: This study aimed to evaluate the effect of an educational program regarding cardiac arrhythmias on nurses' practice in critical care units. Subject and Methods: Design: A quasi-experimental design was utilized in this study. Setting: The study was conducted at Critical Care Units in Port-Said Governmental hospitals (Port Said general hospital, Port -Fouad general hospital and Al zhoor central hospital) recently comprehensive health insurance hospitals in Port Said (El Salam hospital, Al hayah hospital and Al zhoor hospital). Subjects: A convenient sample of available nurses (139 nurses in critical care units divided into 116 female and 23 male) was included in this study. Tools: Tool was used for data collection: Nurses' Practice observational Checklist, which includes part I: Demographic variables, part-II seven Nurses' Practice observational Checklist. Results: The results revealed that, (92.8%) of nurses had satisfactory total practice level immediately post educational program implementation and (69.8%) follow up educational program compared to (37.4 %) of studied nurses pre-educational program implementation. Conclusion: Educational program for nurses had a significant positive effect on improving nurses' practice regarding the care of patients with cardiac arrhythmias. Recommendations: Continuous training and educational program for the purpose of upgrading, improving and updating the practice of the nurses assigned to provide care with cardiac arrhythmias patients.