The invention provides a device for filtering emboli from blood flowing through a lumen defined by the walls of a vessel in a patient's body comprising a filter element. The filter is expandable from a collapsed configuration when the filter element is restrained to an expanded configuration when the filter element is unrestrained, and the filter element comprises a self-expanding material having pores. When the filter element is in the expanded configuration, the average pore size is from 30 to 300 microns and the standard deviation of the pore size is less than 20 percent of the average pore size.