A fistula is defined as an abnormal communication between two cavities or two vessels. Small fistulas (between an artery and another cavity / vessel) without hemodynamic impact (short-circuiting a small amount of blood) should not necessarily be closed. Large fistulas that have a hemodynamic impact (this happens when blood cannot go to the muscles but instead it goes into another cavity or artery) must be closed by a “coil” (fine wire twisted or loop). The metallic loop is mounted via a catheter where the communication is abnormal. The procedure is identical with coronary stent procedure, only that instead of the stent, a wire is implanted.