Abstract Introduction The degeneration of biological valve prostheses is an irreversible process determined by intrinsic factors (calcification, thickening, fibrosis of the leaflets) or extrinsic (prosthesis–patient mismatch, malapposition, prosthetic detachment, thrombosis, endocarditis) that determine hemodynamic dysfunction with frequent need for surgical re–intervention . The average life span of a valve bioprosthesis is around ten years but in some cases premature dysfunction can occur. Clinical Case In September 2021, an 83–year–old woman who was symptomatic of progressively worsening dyspnea entered the emergency care unit of our hospital. In medical history: mitral valve replacement surgery using bioprosthesis in 2016, hypothyroidism in medical therapy. At the entrance, the patient appeared alert, attentive and oriented. Tachypnoic and dyspnoic at rest. Objectively ss 3/6 was appreciated on mitral focus, ss 2/6 on tricuspid focus. Signs of pulmonary congestion. PA 120/80 mmHg. HR 100 bpm, SpO2 88%. Laboratory tests showed increased NTproBNP values. On the ECG: sinus rhythm, HR 96 / min, atrioventricular conduction within limits, narrow QRS, widespread alterations in repolarization as from overload. The echocardiogram performed during the cardiological consultation showed normal biventricular size and contractility. The mitral biological prosthesis appeared in place with an increased transprosthetic gradient (mean Gp 7mmHg) and evidence of severe intraprosthetic regurgitation. There was also moderate to severe tricuspid insufficiency with PAPs estimated at 38 mmHg; the VCI was dilated and non–collapsing. Admitted to cardiac intensive care unit, trans–esophageal echocardiogram was performed which confirmed the finding of bioprosthesis dysfunction caused by severe mitral valve insufficiency in relation to eversion of the posterior leaflet. The patient remained in conditions of haemodynamic instability despite medical therapy with respiratory failure therefore after consulting cardiac surgery she was intubated and transferred for trans–catheter intervention of valve–in valve in emergency. Conclusions Transesophageal echocardiography represents the reference method in the evaluation of valve bioprostheses: in this case it allowed to highlight an unusual mechanism of mitral bioprosthesis dysfunction due to complete eversion of a leaflet.