This study is being conducted to determine what dexmedetomidine does to the body and in turn, what how the body handles the medication. This medication, for the purpose of this trial, is used as a short-term sedative for infants who are immediately post-operative from cardiac surgery and have a breathing tube and are breathing with the assistance of a mechanical ventilator or breathing machine.

This is a single center, dose escalation study of a single bolus dose of dexmedetomidine followed by a continuous infusion for up to 24 hours in infants who are immediately post-operative from cardiac surgery and require tracheal intubation with mechanical ventilation in the post-operative period. Three bolus doses and infusion doses will be administered to a total of 36 evaluable patients.

Inclusion Criteria:

• Patients must be greater or equal to one month or less than or equal to 24 months of age.
• Post operative from cardiac surgery with tracheal intubation/mechanical ventilation in the immediate post-op period.
• Planned tracheal extubation within 24 hours post-operatively.
• Adequate renal function(1-12 months old creatinine less than or equal to 0.6mg/dL and >12 months to 24 months creatinine < or= to 1.0mg/dL)
• Adequate liver function(Total bilirubin < or= 1.5mg/dL and ALT 1-12 months < or = to 165 U/L and > 12 months to 24 months < or = to 90 U/L)
• Isolated heart surgery
• Informed consent

Exclusion Criteria:

• Patients who have received another investigational drug within the past 30 days.
• Receiving continuous infusions of muscle relaxants in the postoperative setting.
• Patients whoo have a positive blood culture without a subsequent negative culture or other evidence of ongoing serious infection.
• Patients, who, int he opinion of the investigator may not be able to comply with the safety monitoring requirements of the study.
• Patients who show signs or symptoms of elevated intracranial pressure.
• Post-operative hypotension based on age.
• Preexisting bradycardia based on age.
• Heart block
• Weight < 5kg
• Patients, who in the opinion of the investigator, are not appropriate candidates for an investigational drug study.

Data collected for up to 30 days following end of dexmedetomidine administration

All adverse events possibly, probably and definitely related are included.