If there is a narrowed area, the catheter is exchanged for an angioplasty balloon. The balloon is advanced to the area of narrowing and then the balloon is inflated. This balloon inside the fistula expands and dilates the narrowing in the vein or the artery. After the angioplasty, another fistulagram is performed to make sure the narrowing has resolved. On rare occasions, a stent (a small metal-mesh tube) needs to be placed to keep the narrowing open.