Transcatheter aortic valve-in-valve implantation represents one interesting therapeutic option for high-risk surgical patients with degenerated bioprostheses. The procedure is less invasive and can be performed without thoracotomy and general anesthesia, if the femoral approach is used. Until recently, failing small bioprostheses could only be treated percutaneously by underexpanding the CoreValve (Medtronic, Inc) or Edwards Sapien valve (Edwards Lifesciences). Underexpansion of these valves might compromise the hemodynamic performance and potentially limit its durability. Herein, we report our initial experience with the 23 mm CoreValve Evolut in 4 patients with degenerated 21 mm Mitroflow valves. The CoreValve prosthesis was successfully implanted in all 4 patients, with no major complications and no mortality at 3-month follow-up exam. However, 2 of the 4 patients developed mildly elevated transvalvular gradients. Therefore, despite our promising results, caution is necessary when considering patients with small degenerated bioprostheses for a valve-in-valve procedure.