Purpose: Delirium is a common symptom among heart surgery patients, and its prevalence is reported to range from 16.0~73.0%. As patients with delirium exhibit multiple negative prognoses, it is important to identify and prevent the risk factors for delirium. However, little research has been conducted to identify the prevalence of delirium and its risk factors among patients who have undergone heart surgery in Korea. Therefore, the aim of this study is to explore the prevalence of delirium and its risk factors in heart surgery patients in the Intensive Care Unit (ICU). Methods: This is a retrospective descriptive correlational study. From 623 patients who entered the ICU after heart surgery in a tertiary referral hospital from September 2016 to August 2017, 421 were selected for this study. Data were collected using electronic medical record. Delirium was evaluated using the Korean Nursing Delirium Screening Scale (Nu-DESC). Results: A total of 63 participants (15.0%) were diagnosed with delirium. Multivariate logistic regression analysis of the variables identified that complex surgery (Odds Ratio [OR]=7.24, 95% Confidence Interval [CI]= 2.80~18.74, p<.001), aortic aneurysm surgery (OR=3.30, 95% CI=1.40~7.77, p=.006), creatinine (OR=2.32, 95% CI=1.17~4.60, p=.016), and ICU length of stay (OR=1.72, 95% CI=1.48~1.99, p<.001) were associated with delirium after heart surgery. Conclusion: The prevalence of delirium after heart surgery in Korean ICU patients is similar to that reported by the American Heart Association study. Type of surgery, lab data, ICU length of stay should be considered in the prevention and management of delirium in heart surgery patients in Korea.