To perform a coronary angioplasty, an x-ray picture, or angiogram of the artery must first be taken. A guide wire is inserted into the femoral artery of the leg and threaded up the aorta to the heart. A “guide” catheter is then inserted over the guide wire and advanced to a position near the coronary arteries. The guidewire is withdrawn and the guiding catheter is manipulated just inside the coronary arteries, one at a time. Contrast (“X-ray dye”) is injected through the catheter allowing a picture of the artery to be taken. Using the angiogram as a reference, a deflated balloon catheter is then guided through the guide catheter to the site of narrowing using a different, thinner guidewire system. The balloon is inflated to open the narrowed artery and flatten the plaque. The balloon catheter and guide wire are then removed.