The purpose of this Phase I study is to determine the safety of a drug called dexmedetomidine (DEX) as part of a balanced general anesthetic and sedative strategy for neonates and infants undergoing corrective cardiac surgery that requires the use of cardiopulmonary bypass for congenital cardiac problems. This study will also design and validate a dosing schema for the use of DEX as described above.

Inclusion Criteria:

1. Male or female, age 0 to 180 days at the time of surgery.
2. Diagnosis of: D-transposition of the great arteries (with or without ventricular septal defect), or tetralogy of Fallot, or ventricular septal defect (with or without associated atrial septal defect and/or patent ductus arteriosus)
3. Scheduled for complete corrective two-ventricle surgical repair with cardiopulmonary bypass.

Exclusion Criteria:

• 1. Less than 37 completed weeks' gestational age at birth for the Neonatal age group (0-21 days); less than 36 completed weeks' gestational age at birth for the Infant age group (22-180 days).

  2. Enrollment in the PHN Collaborative Learning Study, if tetralogy of Fallot 91-180 days of age only.

  3. Known or suspected hepatic dysfunction; AST and ALT >3X upper limit of normal at the time of screening within 72 hours of operation.

  4. Known or suspected renal dysfunction; serum creatinine > 0.8 mg/dL after 7 days of age, >1.2 mg/dL if <7 days of age, within 72 hours of operation.

  5. Preoperative administration of DEX or clonidine within 72 hours of operation.

  6. Major congenital anomaly(ies) outside the cardiovascular system that in the investigator's opinion would potentially affect safety or pharmacokinetics.

  7. Preoperative central nervous system injury resulting in clinical signs and symptoms: coma, seizures, hemiparesis.

  8. Planned period of deep hypothermic circulatory arrest. 9. History of second or third degree heart block. 10. Sinus or junctional bradycardia below 80 BPM sustained for greater than 15 minutes within 72 hours of operation. 11. Junctional rhythm sustained for greater than 15 minutes within 72 hours of operation.

  12. Hypotension defined as mean arterial blood pressure below 35 mm Hg for 0-21 day old neonatal patients, and below 40 mm Hg for 22-180 day old infant patients sustained for greater than 15 minutes within 72 hours of operation.

  13. History of cardiac arrest or ECMO cannulation.