A self-occluding cannula assembly comprising a generally tubular cannula sheath having a connecting hub formed on one end thereof and including an occluding means positioned within the inner bore of said connecting hub. The occluding means comprises (a) a generally frusto conical dilator projection; (b) an elastomeric valving member positioned transversely within the bore of the connecting hub proximal to said dilator projection. The elastomeric valving member is peripherally axially compressed so as to cause displacement, distortion and/or rheological flowing of the elastomeric material thereof in a radially inward direction. An elastically openable and closable aperture is formed in the mid-portion of the valving member and the valving member is alternately movable between an "occluding" position wherein the aperture is closed so as to prevent fluid flow through the cannula and a "non-occluding" position wherein the aperture is open to allow fluid flow through the cannula.
