A surgical stapler, comprising: a handle assembly including a stationary handle, an approximation mechanism, and a firing trigger for firing a plurality of surgical fasteners; and an end effector supported on a distal end of the handle assembly, the end effector comprising: an anvil assembly, comprising: an anvil center rod having a proximal end configured for selective connection to the approximation mechanism and a distal end, the center rod defining a central longitudinal axis; an anvil head secured to the distal end of the anvil center rod, the anvil head including an anvil plate defining a tissue contact surface and a plurality of staple forming pockets formed in the tissue contact surface of the anvil plate wherein at least two adjacent annular rows of the staple forming pockets are nested with one another; and a staple cartridge assembly defining a plurality of staple retaining slots corresponding to a number of the staple forming pockets of the anvil assembly, the staple cartridge assembly comprising a plurality of surgical staples supported therein in a spaced relation to each other; and characterised in that each of the plurality of staple retaining slots and their corresponding staple forming pockets has a curved length corresponding to a curved backspan of each of the plurality of surgical staples. a handle assembly including a stationary handle, an approximation mechanism, and a firing trigger for firing a plurality of surgical fasteners; and an end effector supported on a distal end of the handle assembly, the end effector comprising: an anvil assembly, comprising: an anvil center rod having a proximal end configured for selective connection to the approximation mechanism and a distal end, the center rod defining a central longitudinal axis; an anvil head secured to the distal end of the anvil center rod, the anvil head including an anvil plate defining a tissue contact surface and a plurality of staple forming pockets formed in the tissue contact surface of the anvil plate wherein at least two adjacent annular rows of the staple forming pockets are nested with one another; and a staple cartridge assembly defining a plurality of staple retaining slots corresponding to a number of the staple forming pockets of the anvil assembly, the staple cartridge assembly comprising a plurality of surgical staples supported therein in a spaced relation to each other; and an anvil assembly, comprising: an anvil center rod having a proximal end configured for selective connection to the approximation mechanism and a distal end, the center rod defining a central longitudinal axis; an anvil head secured to the distal end of the anvil center rod, the anvil head including an anvil plate defining a tissue contact surface and a plurality of staple forming pockets formed in the tissue contact surface of the anvil plate wherein at least two adjacent annular rows of the staple forming pockets are nested with one another; and a staple cartridge assembly defining a plurality of staple retaining slots corresponding to a number of the staple forming pockets of the anvil assembly, the staple cartridge assembly comprising a plurality of surgical staples supported therein in a spaced relation to each other; and an anvil center rod having a proximal end configured for selective connection to the approximation mechanism and a distal end, the center rod defining a central longitudinal axis; an anvil head secured to the distal end of the anvil center rod, the anvil head including an anvil plate defining a tissue contact surface and a plurality of staple forming pockets formed in the tissue contact surface of the anvil plate wherein at least two adjacent annular rows of the staple forming pockets are nested with one another; and a staple cartridge assembly defining a plurality of staple retaining slots corresponding to a number of the staple forming pockets of the anvil assembly, the staple cartridge assembly comprising a plurality of surgical staples supported therein in a spaced relation to each other; and