Abstract: 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 can act as a sensor, to monitor an electrical condition of the surrounding cardiac tissue, and to control delivery of the agent responsive to the sensed electrical condition. Several embodiments feature a distal reservoir adjacent the electrode for effecting transient deliveries of the therapeutic agent in minute quantities. Other embodiments are disclosed for providing sustained deliveries of the agents.