A rapid exchange (RX) catheter may provide a proximal seal against a guide catheter inner lumen so that aspiration may be applied through a guide catheter. The catheter may include an exit port that defines a transfer port for aspiration and may enable minimal frictional engagement with the guide catheter proximal of the exit port. Aspiration can be applied to the lumen of the guide catheter and may be directed to and effective at the tip of the RX aspiration catheter. A tip of the RX catheter may facilitate aspiration and retrieval of the clot by expanding under load and can also partially or fully occlude the vessel.