An end effector for fastening tissue including an anvil having a deck to support tissue. The deck has a first surface with a first longitudinal row of staple forming pockets, and a second surface, having a second longitudinal row of staple forming pockets wherein the first surface is positioned vertically above the second surface. The end effector also includes a cartridge having plurality of staple cavities arranged in first and second longitudinal rows. The end effector also includes a plurality of staples removably stored within the staple cavities. The staples include a base, a pair of legs extending from the base, wherein each the leg comprises a tip configured to pierce tissue, and wherein each the leg comprises at least one barb extending therefrom. The end effector also has a firing member configured to lift the staple drivers toward the anvil.
