Abstract: A catheter for ablating and/or mapping tissue on the inner wall of a blood vessel, including a body portion and a tip portion having a proximal section and a distal section, the proximal section including a proximal ablation electrode and a proximal mapping electrode and the distal section including a distal ablation electrode and a distal mapping electrode, wherein the tip portion is deflectable from a first, generally straight, configuration in which the proximal and distal sections are substantially co-linear to a second, J-shaped, configuration in which the proximal and distal sections are generally parallel with a separation therebetween substantially corresponding to the inside diameter of the blood vessel.