Postoperative Pacing for Cardiac Efficiency

Inclusion Criteria: * Age less than 12 years (all potential recruitment). Target recruitment will focus on children less than 12 months at enrollment. Children aged 13-36 months will be eligible for recruitment if we do not meet the target recruitment goals for infants according to the study timeline, and then all patients \< 12 years if recruitment is still below targets. * Scheduled for congenital cardiac surgery at Lurie Children's Hospital * Planned postoperative admission to the CICU * Informed consent obtained from parent(s) or legally authorized representative(s) Exclusion Criteria: * Pregnant patient at time of surgery * Category 2 and category 3 patients on the pulmonary artery reconstruction (PAR) program * Junctional or ventricular rhythm at baseline * Uncontrolled tachyarrhythmia (for example, but not limited to, atrial or ventricular tachycardia, atrioventricular re-entrant arrhythmias) * Hemodynamically significant bleeding, defined as active bleeding that, in the judgment of the treating clinical team, requires ongoing blood product transfusion, surgical or catheter-based intervention, or results in hemodynamic instability requiring escalation of clinical support * Postoperative cardiac arrest prior to protocol initiation or during the protocol period * Requirement for mechanical circulatory support * Requirement for ventricular pacing * Arterial pH less than 7.10 * Determination by the treating clinical team that participation is not in the patient's best clinical interest