A system for ligating the left atrial appendage comprising: a guide catheter comprising: a shaft having a distal end; an alignment element disposed on the distal end of the shaft; and an expandable element provided on the shaft, wherein the expandable element is adapted to expand inside the left atrial appendage; and a ligating catheter for ligating the left atrial appendage, comprising: a hollow shaft having a distal end; a ligating subassembly comprising a plurality of expandable arms arranged in an arcuate configuration and releasably supporting a ligating element thereon, the ligating subassembly being slidably received within the hollow shaft and adapted to move between (i) a retracted position wherein the expandable arms are received within the hollow shaft, and (ii) an extended position wherein the expandable arms project from the distal end of the hollow shaft, with the expandable arms holding the ligating element radially outboard of the shaft when the ligating subassembly is in its second position; and a counterpart alignment element mounted to the shaft, wherein the alignment element on the guide catheter is adapted to couple from inside the left atrial appendage with the counterpart alignment element on the ligating catheter placed outside the left atrial appendage so as to facilitate alignment of the ligating catheter with the guide catheter. a guide catheter comprising: a shaft having a distal end; an alignment element disposed on the distal end of the shaft; and an expandable element provided on the shaft, wherein the expandable element is adapted to expand inside the left atrial appendage; and a shaft having a distal end; an alignment element disposed on the distal end of the shaft; and an expandable element provided on the shaft, wherein the expandable element is adapted to expand inside the left atrial appendage; and a ligating catheter for ligating the left atrial appendage, comprising: a hollow shaft having a distal end; a ligating subassembly comprising a plurality of expandable arms arranged in an arcuate configuration and releasably supporting a ligating element thereon, the ligating subassembly being slidably received within the hollow shaft and adapted to move between (i) a retracted position wherein the expandable arms are received within the hollow shaft, and (ii) an extended position wherein the expandable arms project from the distal end of the hollow shaft, with the expandable arms holding the ligating element radially outboard of the shaft when the ligating subassembly is in its second position; and a counterpart alignment element mounted to the shaft, a hollow shaft having a distal end; a ligating subassembly comprising a plurality of expandable arms arranged in an arcuate configuration and releasably supporting a ligating element thereon, the ligating subassembly being slidably received within the hollow shaft and adapted to move between (i) a retracted position wherein the expandable arms are received within the hollow shaft, and (ii) an extended position wherein the expandable arms project from the distal end of the hollow shaft, with the expandable arms holding the ligating element radially outboard of the shaft when the ligating subassembly is in its second position; and a counterpart alignment element mounted to the shaft, wherein the alignment element on the guide catheter is adapted to couple from inside the left atrial appendage with the counterpart alignment element on the ligating catheter placed outside the left atrial appendage so as to facilitate alignment of the ligating catheter with the guide catheter.