Devices and methods for filtering blood. The devices generally comprise: a mesh for filtering blood flowing within a blood vessel, particularly within an artery such as the aorta; a structure adapted to open and close the mesh within the blood vessel; and a means to actuate the structure. The methods generally include the following steps: introducing a mesh into a blood vessel to entrap embolic material; adjusting the mesh, if necessary, during the course of filtration; and removing the mesh and the entrapped foreign matter from the blood vessel. Additionally, visualization techniques are used to ensure effective filtration.