A microwave antenna is insertable into a cardiovascular catheter and is formed from a coaxial cable including an inner conductor and an inner insulator with the inner insulator having a reduced diameter portion adjacent a distal end of the catheter. An antenna coil portion of the microwave antenna is disposed about the reduced diameter portion and has a first section, a second section, and a point intermediate to the first and second sections. The intermediate point is electrically connected to an outer conductor of the coaxial cable. An impedance matching means is connected to the inner conductor and to the second section of the antenna coil portion.