We reported an adult case of secundum atrial septal defect with severe postoperative pulmonary hypertensive crisis. A 52 year-old female with secundum atrial septal defect and pulmonary hypertension underwent ASD patch closure. After the operation she experienced severe postoperative pulmonary hypertensive crisis. Only administration of PGE1 through the pulmonary artery was effective of hemodynamic improvement and reduction of pulmonary hypertension. Histological diagnosis of lung biopsy showed thromboembolism of small pulmonary artery. Pulmonary hypertension has not been evident during the 3 months since the cardiac catheterization was performed.