Tetralogy of Fallot, due to a ventricular septal defect combined with right ventricular outflow tract narrowing, can display left-to-right, bidirectional, or even right-to-left shunting at the ventricular level. Patients with mild pulmonary stenosis can have left-to-right shunting and usually do not exhibit cyanosis. However, when the pulmonary stenosis is severe, significant right-to-left shunting occurs, and clinically apparent cyanosis becomes evident. Cyanosis is commonly observed in areas rich in capillaries and superficial tissues, such as the lips, fingertips, nail beds, and bulbar conjunctiva.