Abstract: An elongate catheter shaft 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 stiffening structure disposed in the immediate vicinity of the side port aperture. The stiffening structures may be disposed on or be continuous with, for example, an exterior surface, an interior lumenal surface, within a wall of the catheter shaft, or some combination thereof. The stiffening 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.