Background: The role of critical care nurse in arrhythmias management specializes in symptomatic relief, promotion of comfort and taking crisis activity in fatal dysrhythmias. Aim of the study: The aim of the study was to evaluate the effect of training program on nurses' knowledge and practice regarding patient with cardiac arrhythmias in Cardiac Intensive Care units at Zagazig University Hospitals, Egypt. Subjects and Methods: Research design: A quazi experimental design was utilized to achieve the aim of this study. Setting: The study was conducted in Cardiac Intensive Care Units at Zagazig University Hospitals. Sample: A convenient sample of all available nurses (30 nurses) was included in this study. Tools of data collection: two tools were used, Self-administered questionnaire and observational checklists. Data were collected over a period of nine months from November, 2020 to July, 2021. Results: There was statistically significant difference in total level of nurses' knowledge, and practice pre, post and post, follow-up phases of nursing training program. Conclusion: The training program had a significant positive effect on improving nurses' knowledge, and practice regarding patients with cardiac arrhythmias. Recommendations: It was recommended periodic evaluation of nurses' knowledge and practice concerning management of patients in any emergency situation in the critical care units. Keywords: Cardiac Arrhythmias, Nurses' Knowledge, Practice & Training Program.