RF-induced heating of the active catheters was analyzed and analytically modeled to demonstrate that it can be controlled by adjusting the termination impedance. Current distribution of a single-loop active guiding catheter was formulated as a function of the incident electric field, propagation constants, and termination impedances. The tip SAR was displayed on a color-coded Smith chart in terms of the normalized input impedance. For the first time, analytical modeling and transfer function measurements were applied to active catheters. A novel signal level and impedance control unit was introduced, which is applicable also to other interventional devices.