A catlieter has an electrode assembly adapted for use on an ostium and a stabilizing assembly has a balloon member that can be extended distally into the tubular region and inflated to wedge itself in the tubular region for anchoring the electrode assenibly.The balloon member is mounted on an elongated extender that extetids through the catlieter and is provided with longitudinal movetnelit to advance and withdraw the balloon between the stowed and deployed positions.
