The ECG is a non-invasive, effective, simple cardiac test and useful in diagnosing cardiac disorders and detecting any arrhythmia. It plays a critical role in reducing morbidity and mortality in patients with coronary artery disease. Nurses working in critical care areas are responsible for monitoring and interpreting ECGs. Aim of this study is to evaluate the effect of an education program on nurses' performance (knowledge and practice) regarding electrocardiography. Design: A quasi-experimental design was used. Setting: this study was conducted in the coronary units at Benha University Hospital. Sample: all nurses (n = 32) working at coronary units. Tools: Two tools were used a self administered questionnaire sheet to assess knowledge and observational checklist to assess practice regarding electrocardiography. Results: this study showed that the majority of the nurses had unsatisfactory knowledge and practice regarding electrocardiography pre program implementation (96.9% and 87.1% respectively) which improved significally immediately post program (90.6% and 87.5% respectively) p value <0.001, while this improvement lowered slightly post 3 months at follow up (78.1% and 81.2% respectively). Conclusion: the majority of the nurses were having an unsatisfactory performance (knowledge and practice) regarding electrocardiography pre the program implementation. Meanwhile, the majority of the studied nurses had got statistically significant improvement in their performance post the program implementation, while this improvement lowered slightly post three months at follow up, which supported the study hypothesis. Recommendation that the importane of continuous in-service training programs about ECG for the purpose of refreshing, updating the nurses knowledge and practice regarding ECG.