A method of filtering blood in a blood vessel of a patient wherein a catheter is initially introduced into the blood vessel and then advanced to a desired location within the blood vessel. Subsequently, a portion of a positioning assembly having a filter distally attached thereto is guided through the catheter. The filter is then positioned at a location beyond the distal end of the catheter within the blood vessel with the positioning assembly. The positioning assembly is then locked to the catheter. The catheter is then anchored to an object located outside of the blood vessel. Thereafter, an amount of blood is filtered within the blood vessel with the filter. The filter can be readily repositioned by unlocking the positioning assembly from the catheter, repositioning the filter within the blood vessel with the positioning assembly and then relocking the positioning assembly to the catheter.