A 4-year-old boy was diagnosed with pulmonary hypertension by echocardiography at a local hospital. To clarify the cause of pulmonary hypertension, the right heart catheterization examination under general anesthesia was scheduled at our hospital. The pulmonary artery pressures before and after pure oxygen inhalation during the operation were 56/17(34) mm Hg and 60/20(35) mm Hg, respectively, while the aortic pressures were 90/58(65) mm Hg and 94/51(72) mm Hg, respectively. When the patient woke up, he was restless, coughing, and intolerant to tracheal intubation. Then severe cyanosis and hypotension occurred. Emergency bedside cardiac ultrasound: the right ventricle was significantly enlarged, and the left ventricle shrank sharply with decreased myocardial contractility, indicating that a pulmonary hypertension crisis might have occurred. The child’s spontaneous breathing recovered, and vital signs were gradually stabilized after treatment with epinephrine, milrinone, sodium bicarbonate, and hyperventilation. Then, the tracheal tube was successfully removed under deep anesthesia, and the patient was returned to the ward.