Evaluation of Analgesia for Cardiac Elective Surgery in Children

Inclusion Criteria:

* Children aged 3-years - \<18 years
* ASA physical status 1, 2, or 3
* Participant or legal guardian can speak and read English or Spanish
* Undergoing the following cardiac surgeries (Categories 1 \& 2) that are associated with significant acute surgical pain

STS Category 1:

* ASD, PFO closure
* VSD repairs,
* Aortic stenosis sub-valvular repair
* ASD and Partial anomalous venous return repair
* AV canal transitional
* Conduit replacement
* Valve replacement (AVR, PVR)
* TOF repair without ventriculostomy

STS Category 2:

* Glenn shunt (on Bypass only)
* Fontan surgery (on Bypass only)
* Pulmonary artery plasty (main)
* Left Atrium (LA) to Pulmonary Artery (PA) conduit replacement.

Exclusion Criteria:

* Pregnant patients
* Methadone allergy
* Preoperative prolonged QTc more than 460 msec (-30 days to 0 day)
* Subjects undergoing concomitant treatment with known cytochrome P450 inhibitors included in methadone labeling (i.e. macrolides (e.g. erythromycin), azole-antifungal agents (e.g. ketoconazole, voriconazole), protease inhibitors (e.g. ritonavir), fluconazole, SSRIs (e.g. sertraline, fluvoxamine)
* Preoperative opioid use within 30 days before surgery
* History of severe sleep apnea (have a sleep study with an AHI index score more than 10 or clinical signs of sleep disordered breathing - snoring, daytime drowsiness)
* Significant liver, kidney, neurological disease, developmental delay, or any other co-existing medical condition per discretion of the clinical investigator