The filling structure 112 and balloon 116 are expanded and inflated to fill generally half of the aneurismal volume, as illustrated in FIG. 4D. Filling and expansion can generally be carried out as described in U.S. Patent Publication No. 2006/0212112 (Attorney Docket No. 025925-001610US) for one filling structure, except of course that the filling structure 112 will be expanded to occupy only abo