Background: Electrophysiology study could be used to diagnose and treat a variety of arrhythmias effectively. However, little is known about level of knowledge of patients with arrhythmia undergoing cardiac electrophysiology study. Aim of the study: To assess knowledge of patients with arrhythmia undergoing cardiac electrophysiology study. Research design: A descriptive exploratory research design was used to conduct this study. Sample: Sixty-six adult males and females' patients with arrhythmia undergoing cardiac electrophysiology Study. Setting: This study was conducted in the cardiology department at Assuit University Heart Hospital. Tools: Tool (I): Patient's assessment structure interview questionnaire. Tool (II): knowledge assessment questionnaire. Results: More than eighty percentage of the studied patients had unsatisfactory level of knowledge about arrhythmia and electrophysiology study. Conclusion: Based on the present study findings, it could be concluded that patients with arrhythmia undergoing electrophysiology study had unsatisfactory level of knowledge regarding the disease process and electrophysiology study. Recommendations: Develop and implement nursing care standard for patients with arrhythmia undergoing cardiac electrophysiology study and its application of the current study with more participants in other locations around Egypt to generalize the findings.