A medical device formed of a coil with repeating loops, each loop forming a polygon and each successive loop being slightly rotated with respect to its adjacent loops to form a spiral configuration. The polygon in a preferred embodiment is a triangle, and the repeating triangular loop coil can be used as a guidewire in a stent delivering catheter. The guidewire can further include a stiff core wire that is disposed within the triangular loop coil, where the stiff core wire includes tapered sections that reduce the stiffness in the distal direction. The coil can include multiple sections of different loop shapes, including circular, to alter the stiffness of the guidewire to meet the needs of the application.