Embodiments of the invention provide a cannula having a body with a first outer diameter, a proximal end, a distal end, a lumen extending between the proximal and distal ends, and a portion outward of the first outer diameter having a second outer diameter greater than the first outer diameter that is adapted to space tissue from the fluid inlet to maintain fluid flow. Such a cannula is particularly useful for cardiopulmonary bypass procedures using a kinetically assisted venous drainage system.