A 51-year-old male was diagnosed as having an ostium secundum atrial septal defect with severe pulmonary hypertension. Although pulmonary artery pressure was as high as 96/32 and pulmonary vascular resistance was 14.2 U.m2, he underwent corrective surgery, because pulmonary to systemic blood flow ratio was 2.0. After he regained consciousness in ICU, pulmonary hypertensive crises recurrently occurred and the hemodynamics became quite unstable. Administration of conventional drugs proved to be ineffective. Since inhalation of low dose (3-4 ppm) nitric oxide was started, however, his condition was markedly improved and he recovered uneventfully thereafter. Two years later, pulmonary artery pressure was reduced to 52/28 and pulmonary vascular resistance was 9.9 U.m2. Although good outcome can not be expected in all surgically treated cases, we should refrain from deciding easily that surgery is contraindicated, because no criteria of surgical indication for atrial septal defect with pulmonary hypertension appears to be perfect.