A catheter includes a flexible elongated catheter body that defines a needle-receiving, or probe-receiving, lumen, a retractable tissue-penetrable needle, or probe, and an electrode mounted on the distal portion of the catheter body. The needle provides a fluid passage for introducing fluid into tissue to permit the introduction of sclerotic agents for enhancing electrocoagulation of the tissue, heat-responsive drugs for improving the bonding to tissue surfaces, or vaso-constrictor drugs. The probe can also have a passage for fluid. The electrode can provide bipolar electro-coagulation of tissue in combination with an additional electrode mounted on the catheter body, or alternatively, the electrode can be employed in combination with either the needle or probe to establish a bipolar electro-coagulation path through tissue. The needle, or probe, in combination with an external electrode can be used to provide unipolar electro-coagulation, or ablation. In certain instances, the electrode can be used to provide a mapping function inside cardiac chambers.