Guide wire and method for insertion and use of a catheter. The guide wire has a shaft of substantially smaller diameter than the luminal opening, with a flexible coil at one end of the shaft. The guide wire is inserted into the cardiovascular system, and the catheter is advanced along the guide wire to the desired position, with the flexible coil outside the distal end of the catheter. An annular passageway is formed between the shaft and the wall of the luminal opening, and fluids are passed through this passageway while the guide wire is within the catheter. A marker of radio opaque material is provided at the distal end of the guide wire so that the position of the wire can be accurately determined even though the wire itself may be too small to be visible with a fluoroscope.