The most common major clinical signs of tetralogy of Fallot are cyanosis and blood hypoxia. The timing and severity of the clinical signs depend on the degree of right ventricular outflow tract obstruction and the amount of blood flow in the pulmonary circulation. In the short period after birth, cyanosis often does not appear clinically because the ductus arteriosus is not yet closed and blood flow to the pulmonary circulation may come from the unclosed ductus arteriosus. In the vast majority of cases, cyanosis begins to appear weeks or months after birth when the ductus arteriosus is closed and gradually worsens. However, cyanosis may be present after birth if the right ventricular outflow tract obstruction is severe, such as pulmonary atresia, diffuse dysplasia of the outflow tract, and multiple severe stenoses of the funnel, pulmonary valve annulus, and pulmonary valve. If the right ventricular outflow tract obstruction is mild and the right-to-left blood shunt is low, cyanosis is mild, and if the left-to-right blood shunt is predominant at the ventricular level, cyanosis may not be present. The cyanosis increases with eating, crying, and activity, and respiratory distress occurs. The squatting position is preferred by pediatric patients: squatting reduces venous return to the lower extremities and increases the resistance of the body circulation, thereby increasing pulmonary blood flow and increasing arterial oxygen saturation, which reduces cyanosis and dyspnea. In cases of funicular stenosis, when funicular spasm occurs, the stenosis worsens and the sudden decrease in pulmonary blood flow can lead to hypoxic attacks, presenting dyspnea, fainting and convulsions, which can be fatal in severe cases. Seizures are more likely to occur in hot climates and at elevated body temperatures. The jet systolic murmur often decreases or disappears during seizures. Morphine 0.2mg/kg intramuscularly, or insulin 2.5mg/kg daily can relieve hypoxic attacks. In a few cases, due to the large ventricular septal defect, when the pulmonary vascular resistance decreases 1 to 2 months after birth, the left-to-right fractional flow increases leading to congestion in the pulmonary circulation, which can clinically present symptoms of heart failure. However, cyanosis gradually worsens after 6 months of life. In cases of severe cyanosis and significant increase in red blood cells, cerebrovascular thrombosis may lead to hemiplegia or brain abscess. Cerebral thrombosis is more likely to occur when the body is dehydrated. In older cases with severe cyanosis, the bronchial artery is rich in collateral circulation, which may lead to massive hemoptysis if rupture occurs. Signs: The physical growth and development is slow. The face, lips, tongue, and eyelid conjunctiva are obviously cyanotic. Pestle-shaped fingers (toes) are common in children. The turbinate zone is not enlarged and the left anterior chest may be elevated. A jet systolic murmur from right ventricular outflow tract stenosis can be heard between the 2nd and 3rd ribs at the left sternal border and may be accompanied by tremor. In severe stenosis, the murmur is less loud and shorter when the right ventricular blood flow to the aorta is increased and the pulmonary artery blood flow is reduced accordingly. In cases of pulmonary atresia, the systolic murmur may disappear and be replaced by a continuous murmur from the collateral circulation or ductus arteriosus. The second heart sound in the pulmonary valve region is diminished or normal, and may sometimes be a single loud heart sound from the second heart sound of the aortic valve.