coronary ostium and thereafter through the coronary arteries are sharper and shorter radiused the length of the more flexible distal segment 34 is sufficient so that the balloon can reach deeply into the coronary arterial tree without requiring the stiffer proximal tubing 28 to pass through relatively sharp bends such as the bend from a guide catheter to the coronary ostium the distal segment 34 which consists substantially of the thin flexible support wire 44 is able to make the relatively sharp bends with ease thus the only portion of the catheter 12 which actually enters the coronary artery is that which includes the slender support wire 44 this support wire is very flexible and is more easily bent to be able to negotiate shorter radius bends encountered in the coronary arterial tree the catheter is highly steerable due in large measure to the solid wall of the tubing in the elongate proximal segment 28 the tubing is substantially torsionally rigid and tends to transmit substantially all of its rotation applied at the proximal end to the distal end although the intermediate segment of the catheter which includes the slender 0 008 inch diameter wire is too small a diameter to effectively transmit torque over relatively long distances the distal segment 34 is relatively short preferably about 25 cm to 32 cm.