Background: Most children who undergo congenital heart surgery require postoperative mechanical ventilation. Failed extubation (FE) may result in physiologic instability, delay, or set back of the weaning process. FE is statistically associated with prolonged mechanical ventilation. Purpose: We sought to identify frequency, pathogenesis, and risk factors for FE after congenital heart surgery in young children. SETTING: Pediatric intensive care unit. PATIENTS: Children </=36 months of age who underwent congenital heart surgery in the period between January 1998 and July 1999 at our children's hospital. Measurements and Statistical Methods: We performed a retrospective chart review. We defined reintubation within 24 hrs as an FE. Demographic, preoperative, intraoperative, and postoperative data were collected. A modified version of logistic regression, which accounts for lack of independence in data with multiple records per subject, was used to assess the impact of risk factors for FE. A forward selection process was used with p <.05 as the criterion for entry into the model. Estimated odds ratios (EORs) are reported with 95% confidence intervals (CI). The predictive ability of the final model was assessed by using area under the receiver operating characteristic curve. MAIN RESULTS: A total of 212 children </=36 months of age underwent 230 congenital heart operations. Eleven children (5.2%) died perioperatively. After excluding patients who died, there were 219 surgeries among 202 patients; 25.9% (51 of 197), 51.8% (102 of 197), and 72.6% (143 of 197) of patients were successfully extubated by 12, 24, and 48 hrs, respectively. There were 22 cases in which an initial attempt at extubation failed at a median of 67.8 hrs (range, 2.4-335.5 hrs). Five patients failed a subsequent attempt at extubation at a median of 189.5 hrs (range, 115.8-602.5 hrs). The most common causes of initial FE were cardiac dysfunction (n = 6), lung disease (n = 6), and airway edema (n = 3). Risk factors for FE included pulmonary hypertension (EOR, 38.7; 95% CI, 2.9-25.8; p <.001), Down syndrome (EOR, 4.6; 95% CI, 1.8-11.8; p =.002), and deep hypothermic circulatory arrest (EOR, 4.5; 95% CI, 1.3-17.5; p =.018). All were independent predictors of FE (area under the curve, 0.837). The strongest predictor was pulmonary hypertension, which when used alone to predict FE provided a sensitivity of 0.83 (95% CI, 0.59-0.94) and a specificity of 0.75 (95% CI, 0.68-0.80). CONCLUSIONS: Extubation fails after approximately 10% of congenital heart surgery in young patients. Causes of FE are diverse. In our population, preoperative pulmonary hypertension, presence of a congenital syndrome, and intraoperative circulatory arrest are risk factors for FE. Prospective validation of our predictive model with larger numbers and at multiple institutions would improve its utility.