An elongate catheter shaft is provided, having a side port aperture through a side wall of the catheter shaft between proximal and distal ends of the shaft. The side port aperture is open to a lumen. Embodiments of the present invention are directed to attached structures disposed in the side port aperture. The attached structures described herein are directed to biasing the catheter shaft in the region of a side port aperture in a straight or curved configuration that resists undesired flexure in the region of the side port aperture and to providing ease of wire guide passage.