BACKGROUND: Coronary obstruction is a critical risk in valve-in-valve transcatheter aortic valve replacement (TAVR). The UNICORN (undermining iatrogenic coronary obstruction with radiofrequency needle) technique mitigates this risk via intraleaflet valve deployment. However, comprehensive bench testing data regarding this technique is lacking in the literature. OBJECTIVES: The aims of this study were to evaluate leaflet behavior after intraleaflet balloon dilatation across different transcatheter heart valve (THV) platforms, simulate the crossing of a second THV across de novo fenestrations, and understand leaflet behavior during and after deployment. METHODS: In vitro bench testing used 4 index THV platforms: SAPIEN 3, Evolut, Navitor, and ACURATE neo2. Following leaflet traversal, target leaflets underwent sequential balloon dilatation (8-14 mm). We assessed the maximum balloon size tolerated without laceration, the minimum size required for a second balloon-expandable THV (SAPIEN 3 Ultra RESILIA) to cross the fenestration, deployment feasibility, and postdeployment valve geometry. RESULTS: Most index THV leaflets tolerated balloon dilatation up to 12 to 14 mm without laceration. A minimum fenestration size of 12 to 14 mm facilitated most of the second THV crossing. Postdeployment models confirmed coronary clearance on the treated side. Successful intraleaflet THV deployment was achieved with the SAPIEN 3, Evolut, and ACURATE neo2. Conversely, intraleaflet deployment in the Navitor (and Portico) platform was unsuccessful; the leaflet remained intact following expansion, resulting in frame distortion and inner-valve tilting possibly due to stiff leaflet and compliant frame. CONCLUSIONS: This bench study defines optimal balloon sizing for UNICORN across common THV platforms and confirms coronary clearance. It was determined that one index valve resisted intraleaflet deployment. Further clinical validation is required before widespread adoption.