Tetralogy of Fallot is the most common cyanotic congenital heart disease in infancy, accounting for about 12% of all congenital heart diseases. It is caused by malformations of four heart structures: 1. right ventricular outflow tract obstruction; 2. ventricular septal defect; 3. overriding aorta; 4. right ventricular hypertrophy. Its clinical manifestations may include cyanosis, squatting symptoms, clubbed fingers, and paroxysmal hypoxia attacks. Physical examinations generally show delayed development, a prominent precordial area, and at the second to fourth rib interspace along the left sternal margin, a grade 2 to 3 rough systolic murmur can be heard.