An applicator for applying a strap around a vein at the site of a defective venous valve includes a handle portion and a removable cartridge. One end of the strap is anchored on the anvil of the cartridge and the free end is looped around the vein and passed through an opening in the cartridge to overlie the anchored end. The free end of the strap is connected to a strap puller within the cartridge which is coupled to a strap puller extension within the handle when the cartridge is inserted in the handle. The perimeter of the loop is adjusted by moving the tensioner on the handle. When the loop perimeter is at its desired value, the triggers on the handle are pressed to drive a staple through the overlying portion of the strap. A knife within the cartridge cuts the excess strap from the loop.