A system (10) for heating a biological site in a patient's body includes a transformer (14) having a primary winding and a secondary winding. The secondary winding has a tap (24) to provide a ground reference and two sources of radio frequency (RF) energy. An active electrode (16) is connected to each source to apply energy from its associated source to the site, the energy applied by one electrode (16) being out of phase with the energy applied by the other electrode (16).