A 59-year-old man,obese,with history of hypertension, 3 years ago underwent mitral valve (MV) replacement with a mechanical prothesis(Sorin Bicarbon 31) and preservation of the native subvalvular apparatus for severe mitral regurgitation due to anterior leaflet flail. Pre-discharge transthoracic echocardiography (TTE) showed normal prothesis function (mean pressure gradient (PG) 3,2mmHg), no valvular leaks and a normal ejection fraction (EF). Lately, the patient was admitted twice to emergency department for signs of heart failure, solved with increasing dose of oral diuretics. In both cases a TTE showed a normal EF, a trans-prosthetic mean PG of 6,5mmHg and no valvular impairment/leaks. Since the suboptimal TTE acoustic windows, a transesophageal echocardiography (TEE) was recommended. TEE showed a normal motion of both MV discs and no pannus/thrombus or leaks with the use of a 2-beat acquisition protocol. However, with longer observation a pattern of non-cyclic intermittent valve dysfunction was noted: whereas some cardiac cycles showed normal discs’ motion, other cycles demonstrated an emi-disc opening delay or blockage during diastole with significant prolongation of transmitral pressure half-time and higher transvalvular gradient, suggestive of flow impairment. A cine fluoroscopy and a CT assessment were also performed, showing the visible intermittent pattern of valve dysfunction without radiological signs of thrombosis or pannus. At this point, the interference of the MV apparatus with the emidisc was considered the most probable mechanism of dysfunction. A Heart Team decision toward reintervention was taken since the risk of a sudden worsening of the mechanical valve function, with potentially lethal consequences, was considered high. The surgeon at visual inspection confirmed the interference of the subvalvular apparatus with the posterior emidisc motion. The chronic shear stress generated on the mitral remnant likely developed a progressive fibrotic response that determined the thickening of the tissue and the periodical entrapment of the disc. MV prothesis was replaced with resection of the subvalvular apparatus. At dismissal,TTE evaluation showed normal valvular function confirmed at 6 months follow-up. Intermittent prosthetic MV dysfunction is a rare but potentially serious complication of MV replacement with subvalvular apparatus preservation. TEE, cine-fluoroscopy and CT may be useful as complementary tools to detect this rare complication.