OBJECTIVES The objectives of this study were to investigate: (1) the clinical outcome of transcatheter aortic valve-in-valve (VIV) implantation according to Valve Academic Research Consortium (VARC)-2 criteria; and (2) to determine whether postprocedural transvalvular gradients differ in patients with bioprosthesis regurgitation or stenosis as primary mode of failure. BACKGROUND Transcatheter aortic VIV implantation has become a feasible option for selected high-risk patients with failed aortic surgical bioprostheses. METHODS Transcatheter aortic VIV implantation was performed in 14 high-risk individuals at the University of Zurich and University College London. RESULTS The prosthesis was successfully implanted in 13 patients (93%). In 1 patient, a second transcatheter valve needed to be implanted due to valve malpositioning. Thirty-day all-cause mortality was 7% (1/14). Prosthetic valve dysfunction according to VARC-2 at 30 days was observed in 7/14 patients (50%) due to an increased postprocedural transvalvular gradient >20 mm Hg. Preprocedural transaortic gradients correlated significantly with postprocedural gradients (r=0.91; P<.001). At 30-day follow-up, postprocedural gradients were higher in patients with aortic stenosis as primary mode of failure as compared to those with aortic regurgitation (36 ± 6 mm Hg vs 16 ± 4 mm Hg; P=.01). None of the patients exhibited prosthetic valve regurgitation of more than mild degree. CONCLUSION The feasibility and safety of VIV implantation in failed aortic bioprostheses is demonstrated. A higher postprocedural gradient was observed after VIV implantation in patients with aortic stenosis as compared to regurgitation as primary mode of failure.