A prosthesis delivery system having a balloon catheter with an inflatable balloon on its exterior. The balloon is inflatable by injection of fluid through a lumen in the catheter and the balloon is initially partially constrained against inflation by a constraint. A tubular prosthesis is disposed on the catheter over at least a portion of the balloon and a portion of the constraint. The tubular prosthesis has a contracted condition and an expanded condition. The tubular prosthesis is initially disposed on the catheter in the contracted condition. Further, a balloon catheter includes a constraint so that the balloon may be sequentially inflated for dilatation purposes such as in a valvuloplasty operation.