Background: Cardiac catheterization is the gold standard diagnostic test for Coronary artery diseases. Coronary artery diseases are the most common type of heart disease. Patients undergoing Cardiac catheterization, can be extremely intimidating, adequate knowledge and practice about the procedure is critical. Benefit of knowledge and practice acquisition, enhanced self-care, reduced anxiety, increased satisfaction with care and improved pain. Aim of the study: The aim of the present study was to determinethe level of Knowledge and Practice of Patients Undergoing Cardiac Catheterization. Research Design: A descriptive design was used in this study.  And it was conducted at the Cardiac Catheterization Unit, affiliated to Suez Canal University Hospitals in Ismailia. A convenient sample of 100 patients undergoing cardiac catheterization, were assigned. Two tools were used. Tool one: Patients' Interview questionnaire was used to assess patients' knowledge designed by the researcher based on relevant literature review. Tool two: Patient's observational checklists were used to assess patients' practice adapted by the researchers based on relevant literature review. Results: The majority of study population had unsatisfactory level of knowledge and practice with high statistically significance difference as p value < 0.001. Conclusion: Most of study population had unsatisfactory level of knowledge and practice.Recommendation: Application of educational guidelines into training for patients undergoing cardiac catheterization to support knowledge and practice and increase perception and intellectual patients' skills, Educational guidelines on knowledge and practice for other cardiac devices and application of the present study with larger subjects at different places in Egypt to generalize the results.