The aim of this paper is to inform about the experience of the Echocardiography Department of the National Institute of Cardiology Ignacio Chávez, in the assessment of prosthetic valves dysfunction by transesophageal echocardiography. Sixty patients with a total of 75 prosthetic valves: 19 bioprostheses and 56 mechanical valves were studied. Forty four were in mitral position, 27 in aortic position and 4 in tricuspid position. All patients were evaluated using 5 MHz monoplane or biplane transesophageal transducers. The 52% (39) of the studied prosthetic valves were found normally functioning. However, 48% (36) of these showed signs of dysfunction. The causes of dysfunction in the mechanical valves were: obstruction, pannus, infectious endocarditis and periprosthetic leak, and in relation with bioprostheses rupture of the leaflets, stenosis and calcification, partial dehiscence, infectious endocarditis and periprosthetic leak were identified. The obtained percentage and type of prosthetic valves dysfunction in our results agree with those reported in the literature and confirm the great utility of transesophageal research in the detection of the valvular prosthetic dysfunction.