This proposed study attempts to use a microwave antenna in conjunction with a coronary balloon catheter to increase the efficacy of percutaneous transluminal angioplasty. It has been shown that raising the temperature of fibrous, calcified plaque after angioplasty to 95 degrees C often prevents subsequent vessel reclosure. This has previously been accomplished primarily through the user of laser energy. As a possible alternative to lasers, this microwave design will be an easier to use, safer, and less complex method of welding atheromatous plaque following artery dilatation. The antenna will be designed to be a permanent part of the balloon, fitting entirely within the catheter. A coaxial line within the catheter will be used to feed power to the antenna. The power radiated will be constrained such that it is absorbed primarily in the plaque layer, with minimal danger of overheating the surrounding blood vessel well. A carefully chosen fluid will replace that currently used (primarily saline) to inflate the balloon and simultaneously provide the required impedance- matched coupling of field from the antenna to the plaque deposits. The proposed antenna is a narrow helix with many windings and a shallow pitch angle, fed at a frequency of 25 GHz. It will excite electromagnetic modes within the artery that minimize power transfer from the plaque to the artery wall; the wall acts as a reflecting boundary, establishing standing waves in the plaque layer. Knowledge of the precise thickness of the plaque deposits is not required for this microwave system as it is for laser welding. This is an innovative application of microwave technology as well as a drastically new approach to improve the powerful treatment procedure of balloon angioplasty. Extensive literature searches have indicated that microwave plaque welding has not been previously suggested. Although there is no theoretical or experimental data available for this procedure, there is great potential for developing an extremely useful device.