A 5-month-old male infant was diagnosed with congenital heart disease after prenatal examination, which was confirmed as Tetralogy of Fallot (TOF) by echocardiography after birth. Recently, the infant experienced worsening cyanosis of the lips when he cried. The pulse oxygen saturation (SpO2) was 77% with room air. He was scheduled for TOF corrective surgery under general anesthesia. During the surgery, the end-tidal carbon dioxide pressure (ETCO2) quickly dropped when the pulmonary artery was exposed. SpO2 also quickly dropped to 30%, indicating Tet spells. So, pure oxygen ventilation, rapid fluid replacement, correction of acidosis, and intravenous administration of phenylephrine were initiated quickly. Cardiopulmonary bypass (CPB) was also quickly established. After the above treatments, SpO2 was gradually increased. The surgery went smoothly, and the outcome was good.