Disclosed is a catheter to be percutaneously inserted into a living body lumen, which includes a sheath portion having a lumen extending therein, an insertion member slidably disposed in the lumen of the sheath portion and having a distal end portion capable of protruding from a distal end portion of the sheath portion, an injection needle disposed at the distal end portion of the insertion member for injecting a therapeutic composition into a target tissue, and an electrode disposed at a distal end portion of the catheter for measuring a cardiac action potential.