Abstract: The present invention provides for the ablation of obstructions in vessels such as arteries. A catheter having an optical fiber is used to transmit laser energy to the distal end of the optical fiber. The optical fiber is housed in a lumen within the catheter so that it is eccentric with the catheter and also encompasses the center core of the catheter. A second lumen in the catheter houses a steerable guide wire. The optical fiber is substantially aligned with the distal end of the catheter. This catheter assembly is operated by using the steerable guide wire to advance the catheter assembly to the obstruction, turning the laser on, and then rotating the catheter assembly so that energy from the laser which is emitted from the optical fiber ablates an area which is of a larger diameter than the diameter of the optical fiber. This assembly allows for narrow vessels to be cleared of obstructions with only a minimal chance of perforating the vessel walls.