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IN THE past few years several reports on the physiologic changes in ventricular septal defect with increasing age, based on serial cardiac catheterization studies, have appeared in the literature.'-'0 The results of these investigations have not been uniform, and variable conclusions have consequently evolved. A number of workers' 4-6 suggested that progressive pulmonary hypertension and rapidly increasing pulmonary vascular obstruction hardly occur in childhood, whereas others7-9 indicated that these changes are not uncommon at this age. Recently, Lucas et al.'0 demonstrated varying hemodynamic changes in large ventricular septal defects, which they related to variations in the maturation process of the pulmonary vascular bed. This paper is a continuation of previous communications from this Departmentl-3 on the serial hemodynamic findings in ventricular septal defect. To date, a total of 75 patients with isolated ventricular septal defect have had serial cardiac catheterization studies. The results confirm our previous observation that there is a distinct tendency for the elevated pulmonary artery pressure and pulmonary blood flow to fall in the first few years of life. By the second half of the first decade or later, these changes are rarely ob-

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