A system and method for sizing and imaging of cardiovascular defects generally are disclosed capable of producing model images or forms that mimic the shape of defects such as openings or breaches in cardiac septum walls, so that remedial devices of the correct size and shape can be administered to occlude defects. The system uses a three-dimensional open wire imaging structure which is flexible, easy to position and does not occlude blood flow and when expanded, can be measured in situ.