A system is disclosed, for administering a therapeutic agent locally and to a depth within cardiac tissue. An elongate, flexible catheter contains a flexible electric conductor and supports at its distal end an implantable electrode incorporating a penetrating element, typically a fixation helix or a linear needle that penetrates cardiac tissue as the electrode is implanted. A therapeutic agent is delivered through the electrode, to the cardiac tissue surrounding the penetrating element. The electrode acts as a sensor, electrically coupled through the flexible conductor, and monitors an electrical condition of the surrounding cardiac tissue. A controller is coupled to the sensor and to a pump or reservoir containing the therapeutic agent, to control delivery of the agent responsive to the sensed electrical condition. The implanted electrode further can be used to deliver RF current to ablate the surrounding tissue. Several embodiments feature a distal reservoir adjacent the electrode, for effecting transient deliveries of the therapeutic agent in minute quantities or chronic delivery of growth factors. Another embodiment incorporates a bilumen catheter and a set of unidirectional valves, to facilitate changing therapeutic agents or purging the catheter of an agent after delivery.