Background: Pain following cardiac surgery is a multifaceted phenomenon resulting from a number of mechanisms. High-levels of post-operative pain are associated with cardiovascular and respiratory complications and adequate pain management is crucial for enabling fast recovery. Aim of the study: to assess the severity of pain among post cardiac surgery patients. Design: descriptive design was used in carrying out the study. Setting: The study was conducted Al-Hayat Hospital El- Fayoum in the Open Heart Surgery Intensive Care Unit. Subjects: A purposive sample of newly admitted adult post cardiac surgery patients to open heart surgery intensive care unit. Tools: structured interview questionnaire and Subjective and objective Pain Assessment Scale. Results: this study represent high percentage of severe pain among post cardiac surgery patients . Conclusion: it can be concluded that, cardiac surgery patients suffered from severe pain during the procedural pain. Recommendation: it's recommended for design different nursing interventions protocol to reducing the severity of pain among post cardiac surgery patients.