A filter and method for trapping emboli during endovascular procedures are provided. In one embodiment of the invention, the filter is formed from a bent, flexible guidewire shaped to define a frame and a porous filtering material mounted to portions thereof. In a collapsed state, the filter can readily pass through the lumen of a catheter and into the bloodstream of a patient. Upon completion of an endovascular procedure, the filter is collapsed and retracted into the catheter. In alternative embodiments of the invention, porous filtering material is mounted to external portions of a catheter, and a control guidewire is provided to selectively expand the filter between open and closed states.