Records of 140 infants younger than 2 yr of age who had undergone open heart surgery were studied to evaluate the duration of postoperative mechanical ventilation (MV), to determine the relationship between prolonged MV and mortality, and to identify variables predisposing the patient to prolonged MV. MV was required beyond the first postoperative day in 56 infants, and was prolonged for at least 7 days in 19 infants. Mortality was approximately the same (16% to 17%) whether or not MV was required for more than 7 days. Preoperative and intraoperative variables associated with longer MV included younger age, longer cardiopulmonary bypass time, longer aortic cross-clamp time, and preoperative MV. Multiple predisposing factors increased the probability of prolonged MV. Postoperative variables including premature extubation and a second surgical procedure also were associated with prolonged MV. The consequences of prolonged MV may be minimized by early nutritional support, aggressive surveillance for treatable complications, and avoidance of premature extubation.