Tubular graft

1. A tubular graft comprising:

a tubular section defining an interior and having an internal surface, a first end defining a first orifice and a second end defining a second orifice, each of the first and second orifices leading to the interior of the tubular section; and

an internal helical formation for imparting a helical flow on fluid passing through the tubular graft, wherein (i) the first end of the tubular graft is tapered such that the first orifice defined by the first end has an inner base and an outer tip, (ii) the internal helical formation terminates at the first orifice within a 180° arc centered on the inner base of the first orifice, and (iii) the tubular graft comprises only one internal helical formation that terminates at the first orifice,

wherein the tubular graft further comprises an external helical formation for supporting the tubular graft, and the external helical formation has a helix angle greater than 50°.

2. The tubular graft of claim 1 wherein the first end of the tubular graft is tapered sinusoidally such that the first orifice is egg-shaped, the radius of curvature at the outer tip being smaller than the radius of curvature at the inner base.

3. The tubular graft of claim 1 wherein the internal helical formation terminates at the first orifice within a 120° arc centered on the inner base.

4. The tubular graft of claim 1 wherein the internal helical formation terminates at the first orifice within a 60° arc centered on the inner base.

5. The tubular graft of claim 1 wherein the internal helical formation terminates at the first orifice at the inner base.

6. The tubular graft of claim 1 wherein the internal helical formation is a ridge which extends inwardly from the internal surface of the tubular graft.

7. The tubular graft of claim 1 wherein the external helical formation has a helix angle between 65° and 80°.

8. The tubular graft of claim 1 wherein the second end of the tubular graft is tapered in the same way as the first end.