Methods and devices for implanting pacing electrodes or other apparatus, or for delivering substances, to the heart of other tissues within the body. A guided tissue penetrating catheter is inserted into a body lumen (e.g., blood vessel) or into a body cavity or space (e.g., the pericardial space) and a penetrator is advanced from the catheter to a target location. In some embodiments, a substance or an apparatus (such as an electrode) may be delivered through a lumen in the penetrator. In other embodiments, a guidewire may be advanced through the penetrator, the penetrating catheter may then be removed and an apparatus (e.g., electrode) may then be advanced over that guidewire. Also disclosed are various implantable electrodes and electrode anchoring apparatus.