The haemodynamic and angiocardiographic data of 19 patients with Starr-Edwards mitral valve prosthesis were analysed to determine the causes of secondary deterioration observed in 14 of them. This was shown to be due to: 1. Surgical complications or progression of pre-existing valvular lesions which were not, or only partially, corrected (3 cases) (adiastole due to pericardial effusion, aortic valve disease and severe tricuspid incompetence); average diastolic pressure gradient CPW-LV 4.7 +/- 1.5 mmHG, the functional valve surface area (FVA) 1.37 +/- 0.2 cm2, LVEDP 17.7 +/- 4 mmHg, LVEDV 57.5 +/- 11 ml/m2, and EF 73.5 +/- 8 p. 100; 2. Deterioration of left ventricular contractility with LVEDP greater than 13 mmHg, LVEDV greater than 100 ml/m2 and EF less than 45 p. 100 (4 cases); CPW-LV gradient 9.8 +/- 4 mmHG, FVSA 1.30 +/- 0.2 cm2, LVEDP 20.5 +/- 8 mmHG, LVEDV 212 +/- 168 ml and EF 38 +/- 21 p. 100; 3. Significant reduction of left ventricular volume (LVEDV 22 ml/m2 1 case); 4. Left atrial thrombosis (1 case); 5. Prosthetic valve dysfunction (5 cases) one paravalvular leak and 4 thromboses. In these 4 cases, the PCW-LV gradient was 15 +/- 5 mmHg, FVSA 0.95 +/- 0.1 cm2 LVEDP 8 +/- 2 mmHg, LVEDV 132.8 +/- 93 ml/m2 and EF 45 +/- 28 p. 100; these results were different to whose found in the other patients and those investigated systematically (PCW-LV gradient 8.2 +/- 3 mmHg, FVSA 1.38 +/- 0.3 cm2, LVEDP 11 +/- 4 mmHg, LVEDV 66.4 +/- 33 ml/m2, EF 53 +/- 13 p. 100). The significant haemodynamic criteria in favour of thrombosis of the prosthesis were: CPW-LV gradient greater than 12 mmHg under basal conditions or after exercise and a FVSA less than 1.1 cm2.