Aspects of the disclosure include sizing catheters and methods for determining the size and other physical parameters of an internal orifice or lumen. Embodiments include a sizing catheter assembly having a handle assembly and a catheter assembly including at least one catheter extending from the handle assembly. The catheter assembly also includes at least two sizers, which can be adjustably spaced from each other. Each of the sizers are configured to conform to respective portions of a lumen of a patient's anatomy. The sizing catheter is configured such that the sizers are configured to specify or determine first and second dimensions of the lumen and also distance between the sizers. The sizers can include valve leaflets or the sizing catheter can include a temporary valve. Additional aspects include software/methods of assessing and determining an appropriate implantable device that can include assessing the biomechanical interaction between the device and the anatomy.
