A child with large perimembranous VSD has congestive hea failure. What may be the cause of improvement of failure in this patient

Patients born With uncomplicated VSD may develop pulmonary stenosis due to hyperophy of right ventricular infundibulum ,develop pulmonary aerial hypeension or rarely develop aoic regurgitation. Development of pulmonary aerial hypeension is dreaded complication since if it is of obstructive type the patient becomes inoperable. Ref Ghai pediatrics eighth edition pg no 417