Background <p>After mitral valve replacement with preservation of the subvalvular apparatus, prosthetic dysfunction resulting from retained native structures is extremely rare. When it occurs, it may directly threaten the patient’s life. We report an unusual case of severe regurgitation resulting from preserved chordal rupture. The key distinction of this case is the presentation of late, severe continuous prosthetic regurgitation and reversibility.</p> Case presentation <p>A 54-year-old man had undergone double mechanical valve replacement for severe rheumatic mitral stenosis with mild regurgitation and concomitant aortic regurgitation three years earlier. During surgery, the posterior mitral leaflet and its entire subvalvular apparatus were preserved. Current transesophageal echocardiography revealed a mobile, cord-like structure between the lateral occluder and the prosthetic sewing ring, interfering with leaflet excursion and preventing full closure. This was accompanied by severe prosthetic mitral continuous regurgitation. Surgical findings revealed a ruptured chordae tendineae at the papillary muscle attachment, with the remnant preventing leaflet coaptation. Surgical excision of the ruptured chordal remnant successfully restored normal leaflet function, with complete resolution of the regurgitation confirmed on intraoperative transesophageal echocardiography.</p> Conclusions <p>When obstruction or regurgitation develops after valve replacement with subvalvular preservation, uncommon causes—such as residual subvalvular tissue or ruptured chordal entrapment—should be considered after excluding more common etiologies. This case illustrates the critical role of transesophageal echocardiography in the diagnosis of chordal entrapment after mitral valve replacement and potentially in preventing complications. The potential benefit of preserving the subvalvular apparatus warrants thoughtful deliberation. Surgical removal of the offending tissue or valve replacement remains the definitive treatment.</p>