To determine the frequency of postoperative fever in children with congenital heart disease who undergo cardiovascular surgery, and the risk factors associated. In a prospective cohort study, 100 children under the age of less than 9 years were followed-up during hospitalization in order to detect fever after cardiac surgery. Preoperative, perioperative, and postoperative variables were assessed to determine their relationship with postoperative fever. The cases were patients who developed fever. Multivariate analysis was used, and the odds ratio (OR) and 95% confidence intervals (95% CI) were calculated. The frequency of postoperative fever was 46%. Fever appeared within 24 hours of surgery in 56% cases. In 32/46 (70%) cases, fever remitted within 72 hours. Fever was more common in patients who underwent open-heart surgery than in those treated with a closed technique (28 vs. 18, P = 0.045). Prolonged extracorporeal circulation (OR = 1.024; 95% CI, 1.004-1.045), aortic cross-clamping (OR = 2.83; 95% CI, 1.21-6.61) and postoperative infections (OR = 24.07; 95% CI, 7.2-75.0) were the risk factors associated with the development of postoperative fever. Postoperative fever is common in children with congenital heart disease. The identification of risk factors associated to the development of fever should help clinicians to identify the cause of fever in this group of patients.