Open sternotomy (OS) after cardiac surgery involves leaving the sternum unapproximated and closing the skin with a patch, then closing the chest 2-3 days later after the patient (pt) has stabilized. OS has been shown to be safe and effective in adults and children, but there is little published data on the management of OS with delayed sternal closure (DSC) in neonates. From 7/92 to 6/95 OS was performed in 60 neonates who underwent surgery on cardiopulmonary bypass for congenital heart disease. Indications for OS were: routine OS in patients with hypoplastic left heart syndrome (18), bleeding(14), ventilatory compromise (5), hemodynamic instability (23; 6 of whom also had bleeding or ventilatory compromise as an indication), and VAD/ECMO placement (6). OS was elected in the operating room without a trial of chest closure in 96% of pts. Most of these pts were critically ill and underwent complicated operations (76% had Norwood, arterial switch, truncus repair, tetralogy of Fallot repair, or Ross procedures) with prolonged periods of bypass (219±99 min). 13 pts died prior to DSC, 11 within 2 days of surgery. DSC was performed a median of 3 days after OS (1-26 days) in the remaining 47 pts, 6 of whom died in the hospital (all with OS >6 days). Central venous pressure decreased significantly (p=.02) from postoperative day 1 (8.6±2.0 mmHg) to immediately pre-DSC (7.1±2.4 mmHg), and increased significantly (p<.0001) following DSC (9.6±2.3 mmHg). After DSC, respiratory rate (p=.03), inspiratory pressure (p<.0001), mean airway pressure (p<.0001), and FiO2 (p=.02) all had to be increased significantly. Postoperative mediastinal infections occurred in 3 pts, all of whom had complicated postoperative courses and prolonged OS (11,14, 26 days), and required rectus abdominis flap sternal reconstruction. 2 of these pts expired. One other patient developed a superficial (but culture negative) wound infection. Wound complications occurred in only 1 of 40 pts who underwent DSC within 1 week of OS, which is similar to rates of superficial wound infection in young pts without OS. In general, OS with DSC is a safe and effective procedure to improve early postoperative hemodynamics and hemostasis after neonatal cardiac surgery, particularly when DSC is performed within 1wk of surgery.