Lockout mechanism for a surgical stapler

A surgical stapler comprising:

• a) a handle assembly including an elongated barrel portion and an actuation handle mounted for manipulation through an actuation stroke cycle which includes a clamping stroke segment and a stapling stroke segment;
• b) an elongated body extending distally from the barrel portion of the handle assembly and defining a longitudinal axis;
• c) an elongated actuation shaft supported at least in part within the barrel portion of the handle assembly and mounted for longitudinal movement in response to manipulation of the actuation handle;
• d) a disposable loading unit removably operatively engaged at a distal end portion of the elongated body and including a staple cartridge containing a plurality of staples mounted in a base, an anvil mounted adjacent the staple cartridge and movable between an open position and a clamping position, and an actuator including a drive beam and a drive block which drive block operatively engages with the elongated actuation shaft and is movable in a distal direction relative to the staple cartridge and anvil to effect movement of the anvil from the open position to the clamped position during said clamping stroke segment and to effect sequential ejection of the staples from the cartridge during the stapling stroke segment;
• and
• e) a lockout mechanism mounted in the disposable loading unit, said lockout mechanism including a lock mounted on the drive block for longitudinal reciprocal motion therewith, the lock being pivotal between an unlocked position and a locked position, the lockout mechanism further including fixed support structure formed in the base for supporting the lock in the unlocked position during the clamping stroke segment of the actuator and a projection formed in the base for engaging the lock in the locked position upon retraction of the drive block to move the anvil to the open position after firing.