103 patients (52 males, 51 females) suffered from ventricular septal defect associated with pulmonary hypertension were operated on under sardiopulmonary bypass from 1981-1995 at high altitude. The age of the patients ranged from 2 to 29 years. The ratio of pulmonary systemic arterial pressure was more than 0.91 (0.91 to 1.21). The defects were closed by using dacron patch. The operative mortality was 4.8% among the survivals. 98 patients were followed up for a period from 3 months to 3 years (mean 2.4 years). Excellent results were observed in 93 patients, and good in 4. There was a late death. On account of the improvement in surgical technique, myocardial protection and postoperative care, the result of operation was improved markedly.