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Serial cardiac catheterization has been performed in 75 patients with isolated ventricular septal defect. At the time of the first cardiac catheterization, 39 were under 1 yearof age, 19 were between 1 to 3 years, 14 between 3 to 10 years, and three over 10 years. In 68 patients the second catheterization was performed 1 to 7 years after the first, and in seven patients a third cardiac catheterization was performed 2 to 5 years after the second.Normal pulmonary artery pressure was observed at the initial study in 25 patients. Of these, only one revealed a slight rise in pulmonary artery systolic pressure by 19 mm. Hg; the rest revealed no significant hemodynamic changes.Mild pulmonary hypertension (31 to 59 mm. Hg systolic pressure) was noted in 28 patients at first catheterization, at which time moderate or severe pulmonary hypertension (60 mm. Hg or more systolic pressure) was present in 22 patients. In 33 of these 50 cases, the initial investigation was done during infancy and not later than the second year. In three fourths of the cases with mild pulmonary hypertension, and in two thirds of those with moderate or severe hypertension studied at this very early age, a significant drop in pulmonary pressure and flow was observed at the subsequent catheterization. This was interpreted to indicate most likely relative reduction of the functional size of the defect during early childhood. In eight patients hemodynamic and angiocardiographic evidence of the ventricular septal defect disappeared, indicating probable functional closure.Progressive pulmonary vascular obstruction was observed in six patients, one of whom already had Eisenmenger's complex at the initial examination. All but one, an 11-month-old infant, had significantly elevated pulmonary vascular resistance already present during the first cardiac catheterization. In seven patients with similar findings at the initial examination, striking reduction in pulmonary vascular resistance was observed. The progressive pulmonary vascular obstruction is interpreted to indicate failure of the pulmonary vascular bed to undergo maturation, whereas the diminution in pulmonary resistance observed in the other group is interpreted to indicate delayed onset of pulmonary vascular maturation.The therapeutic significance of these findings is discussed.

Further Observations on the Natural History of Isolated Ventricular Septal Defects in Infancy and Childhood