Tetralogy of Fallot (TOF) is one of the most common complex congenital heart diseases of newborns. In the presence of TOF, it is vital that creation of a shunt between the pulmonary and systemic circulations. The objective of this study is to use computational fluid dynamics (CFD) approaches to simulate flow variations in patients of TOF before and after the operation. Knowledge of the flow conditions may be helpful in the clinical management of these patients, whose survival is critically dependent on the blood flow distribution between the pulmonary and systemic circulations.