There are 6 common types of congenital heart diseases with right-toleft lesions: tetralogy of Fallot (TOF), transposition of the great arteries, truncus arteriosus, tricuspid atresia, total anomalous pulmonary venous return, and pulmonary atresia with intact ventricular septum. Tetralogy of Fallot Tetralogy of Fallot is the most common intrinsic cyanotic congenital heart disease, which accounts for 5% to 10% of all congenital heart disease and has a prevalence of about 1 out of 2,000 live

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... . 1 Anatomy and Pathophysiology Tetralogy of Fallot comprises a constellation of cardiac findings that share the following common anatomic abnormalities (Fig. 1) : a large malaligned ventricular septal defect (VSD), overriding of the aorta over the septal defect, right ventricular outflow obstruction, and right ventricular hypertrophy. The anatomic spectrum of TOF is diverse and includes other variants such as pulmonary stenosis (TOF-PS), pulmonary atresia (TOF-PA), or absent pulmonary valve (TOF-APV). The pathophysiology of TOF depends, primarily, on the degree of right ventricular outflow tract obstruction (RVOTO) and, secondarily, on the status of the systemic vascular resistance relative to the degree of right ventricular obstruction. The patients can be fully saturated or severely cyanotic depending on the ratio of pulmonary to systemic blood flow. In a Tetralogy spell (tet spell), or hypoxic spell, the infants experience episodes of severe hypoxemia and acidemia. The responsible factors may be increase in RVOTO and increase in oxygen requirement, decrease in peripheral vascular resistance, contraction of the right ventricular infundibulum, closure of the ductus arteriosus, or development of physiologic anemia. [2] [3] [4]