Background: Unplanned 30-days readmission post cardiac surgery impose higher risk for complications, increased cost and unfavorable event both for the care provider and the patient. This study is to determine the unplanned readmission rate, determinants and most common events within thirty days post cardiac surgery . Recommendations to prevent or minimize these complications are included. Method : Sitting and design: A retrospective record review was conducted among all the adult patients who underwent open heart surgery between January 2020 and December 2021at King Abdulaziz University Hospital (KAUH), Jeddah, Kingdom of Saudi Arabia. methods and material: Using Google Forms, we manually collected data from hospital records. statistical analysis used: binomial logistic regression model (using the backward stepwise method). Regression outcomes were expressed as odds ratios (ORs) and 95%CIs. A p value of < 0.05 indicated statistical significance. Results: Among 400 patients who underwent cardiac surgery, 343 patients were included in the study, 53 unplanned readmission, rate of 16.3% (95%CI, 12.8 to 20.6%). The most frequently reported reasons for readmission were sternal wound infections (7.3%), pleural effusion (2.0%) and heart failure (1.7%). Female gender, high post operative LDH and urea are the most important risk factors. Conclusion: Discharge planning, patient education, and cardiac surgery nurse home visit constitute the most important factors to minimize 30 days of unplanned readmission.