A device and method for inserting a variable stiffness catheter into a subject with a catheter body being in relatively stiff state at a first temperature and a more flexible state at a second temperature. A temperature sensitive polymer is incorporated into the catheter that varies in stiffness depending on the temperature. The stiffness of the catheter is regulated by being in thermal contact with a circulating fluid within the catheter, or by being connected to resistive members in thermal contact with temperature sensitive alloys or polymers. The variable stiffness catheter can therefore be guided through the vasculature while in a relatively flexible state, but be changed into a relative stiff state during ablation procedures.
