Malformations of the heart (congenital heart disease) are the most common congenital birth defects, occurring in about 1% of children. Each year, between 150-200 children will undergo open heart surgery at British Columbia Children's Hospital (BCCH) to repair the defect(s) in their heart. The abnormal structure of the heart or the open heart surgery may cause damage to the electrical system of the heart which can disturb the rhythm of the heart (arrhythmias), prolong recovery or be life-threatening. For this reason, temporary pacing wires are placed in the heart following surgery to ensure the heart rhythm is as normal as possible during the post-operative period (pacing). In recent years, scientists have recognized that pacing the heart from one area is not necessarily the same as pacing it from a different area. In fact, in some individuals with arrhythmias and poor heart function, pacing the heart from different areas can improve the pumping of the heart, resulting in better heart function. This form of treatment is called Cardiac Resynchronization Therapy (CRT) because it endeavours to optimize the pumping of the heart by changing the electrical activation of the heart. CRT has been used to a very limited extent in children. A few pediatric cardiologists have used CRT to help children who are in heart failure. We would like to determine whether pacing the heart from different areas after open heart surgery improves the child's heart function and aids his or her recovery.