Paper presents the cause of 54-year-old patient with implanted mechanical heart valve prosthesis in the mitral position admitted to the hospital with a serious left ventricle (LV) systolic dysfunction. Patient underwent repeated attacks of acute left-sided heart insufficiency on the basis of verified thrombosis of the mechanical heart valve prosthesis. Pharmacological treatment was not effective and the systemic thrombolysis failed. Patient was twice reoperated – thrombectomy was performed during the first surgery, mechanical heart valve prosthesis was replaced with biological prosthesis during the second one. Patient was permanently treated with anticoagulants. The combination of bioprosthesis in the mitral position with the anticoagulant treatment appears to be a final therapy of the patient

        Key words: mechanical heart valve prosthesis, thrombosis of the mechanical heart valve prosthesis, heart failure.