Guidewires and methods for transmitting electrical stimuli to a heart and for guiding and supporting the delivery of elongate treatment devices within the heart are disclosed. A guidewire can comprise an elongate body, including first and second elongate conductors, and at least first and second electrodes. A distal end portion of the elongate body can include a preformed bias shape, such as a pigtail-shaped region, on which the first and second electrodes can be located. The preformed bias shape can optionally be non-coplanar relative to an intermediate portion of the elongate body. The first and second elongate conductors can be formed of a single structure or two or more electrically connected structures. The conductors can extend from proximal end portions to distal end portions that electrically connect to the first and second electrodes. A corewire can extend the length of the elongate body, can at least partially form the first conductor, and can be at least partially surrounded by the second conductor.