Pulmonary hypertension is seen in infants and young children who have congenital heart defects resulting in excess pulmonary blood flow. The critical care nurse can implement several interventions in the immediate postoperative period to help prevent the potentially lethal complication of pulmonary hypertensive crisis in a cardiac surgery patient. Respiratory interventions include hyperventilation, maintaining an alkalotic pH, supplemental oxygen, and low positive end-expiratory pressure. In addition, the nurse must consider the serum potassium, hematocrit, and patient temperature, and administer appropriate medications.