An active system for deflecting a distal portion of a catheter into a hoop configuration includes an elongated catheter body having a proximal portion and a distal portion that is formed with a lumen. A thin-walled tube, which is typically made of a metallic material, is positioned in the lumen. The tube includes a cylindrical wall and includes a plurality of lateral slits that are typically formed in the tube wall and arranged such that the tube can be transformed between a relaxed, cylindrical configuration and a deflected configuration wherein the tube is substantially hoop shaped. One end of a deflection wire is attached to the tube and the other wire end is attached to a reel that is rotationally mounted onto a catheter handle housing. In use, the reel is rotated to axially retract the wire and transform the tube into a hoop configuration.