Abstract: Devices and methods for assessing the size, shape, and topography of vessel lumens and hollow portions of organs are described. The devices and methods are particularly adapted for determining the size, shape, topography, and compliance of the native heart valves to facilitate the later implantation of a prosthetic heart valve. The devices are typically catheter-based having an assessment mechanism fixed to a distal end of the catheter. The assessment mechanism generally includes an expandable member, such as a balloon. The assessment mechanism may also include an imaging member, a physical assessment member, an electronic mapping construction, an alignment mechanism, a valvuloplasty balloon, or any combinations thereof. The methods typically comprise deploying the balloon percutaneously to a target location, expanding the balloon, and determining one or more physical parameters associated with the target location.