Suggest Treatment For Congenital Under Developed Artery

Our premature granddaughter born at 30 weeks has an artery that doesn't open enough (keeps tightening). Was told that it is because the artery isn't developed enough. I have questions but don't want to worry my son needlessly. I hope you can help. The cardiologist says they will be doing an angioplasty to open the artery. I understand that but, if the artery isn't developed what good will that do? Should something else be considered. He also said that if that doesn't work, that artery replacement isn't done on infants.? What might happen next? Thank you