The present invention is a clinically practical, rotational angioplasty system which employs a unique rotary ablative device for mechanically abrading, and thereby removing, lesions from within a patient's vessels. The device has a gas driven prime mover connected, via a hollow helical drive assembly, to an ellipsoidal, rotating, ablative burr which is used for the actual recanalization of the patient's vessel. The burr is provided with a central opening therethrough, which, together with the hollow drive assembly, permits the burr and drive assembly to be threaded over a guide wire similar to the type conventionally used in a catheterization procedure. The drive assembly is located within a hollow sheath which prevents the rotating drive assembly from contacting the inner walls of a patient's vessel.