A rapid exchange aspiration catheter includes a distal portion with a round cross-sectional shape, taken transverse to a longitudinal axis of the catheter. A primary lumen through the catheter has a size and a shape, and extends through the catheter at a location that are optimized for aspiration. In particular, the size of the primary lumen is maximized relative to the outer diameter of the catheter by minimizing the thicknesses of interior walls of the catheter. Such optimization maximizes the rate at which fluid flows through the aspiration catheter without compromising the ability of the catheter to withstand negative pressure (i.e., a vacuum). The present invention also includes systems in which the catheter is used in conjunction with a guide catheter and a wire, systems in which the catheter is used in conjunction with an aspiration element, and methods of using the catheter.
