PURPOSE: To enable the expansion of a blood vessel of a heating system by using an ordinary catheter for PTCA.

CONSTITUTION: A guide wire 1 is formed by passing a constantan wire 8 into a stainless steel pipe 6. The front ends of the stainless steel pipe 6 and the constantan wire 8 are soldered to constitute the measuring contact of a thermocouple. The outside surfaces of the stainless steel pipe 6 and the constantan wire 8 are coated with 'Teflon(R)'. The front end of the stainless steel pipe 6 has no coating and constitutes an electrode part 7. The guide wire 1 is passed into the lumen of the body of the catheter for the PTCA at the time of expanding the blood vessel. The constricted part of the blood vessel is expanded while this part is heated by inflating a balloon and passing a high-frequency current to the guide wire 1.