How do i know when will they do surgery to fix pulmonary valve stenosis?

Depends on severity: Pulmonary stenosis can often be "fixed" in the cath lab with a balloon catheter. Mild stenosis is well tolerated and can often just be left alone. Surgery is used usually only after a balloon procedure was unsuccessful. Of possible more concern is the amount of pulmonary leak or regurgitation and the effect that this has on the right ventricle which may require pv replacement.