Various methods and devices are provided for penetrating tissue. In one embodiment, a tissue-penetrating device is provided and includes a flexible elongate shaft and a flexible elongate wire extending through the elongate shaft and having a needle tip at a distal end thereof for penetrating tissue. The needle tip can be conductive and the elongate wire can be adapted to couple to an energy source for delivering energy to the needle tip to facilitate penetration of the needle tip through tissue. The device can also include a protective sheath disposed over at least a portion of the elongate shaft and movable relative to the elongate shaft between a distal position and a proximal position. The protective sheath is configured to either protect the needle tip or electrically isolate the needle tip after the needle tip is penetrated through tissue, thereby preventing unintentional penetration of adjacent tissue.
