Abstract: A guide wire for guiding a medical device within a patient is disclosed. The guide wire includes an elongate core with a flexible body disposed about and secured to a distal core section of the elongate core. A shapeable member extends distally from the distal core section, and the shapeable member preferably includes a nonrectangular, cross-sectional shape including a D-shape, semicircle, a triangle, or the like. In various embodiments, the polygonal shape of the cross-section is defined by a height h and a width b, wherein the moment of inertia of the shapeable member is preferably defined by at least 0.083×b×h3.