Once a fistula is created (vein is connected to the side of an artery), it usually takes about 2 months before the fistula is mature and ready to start using for dialysis. If the fistula is slow to mature, a fistulagram is done to identify the cause. If there is a narrow area present limiting flow in the fistula, balloon angioplasty will be performed to promote maturation. Sometimes there are large branches present taking flow away from the fistula. If this is causing the fistula to be slow to mature, a coil can be placed into this branch to stop flow in the branch in order to have all the flow going into the fistula.