Impairment of the left ventricular ejection induced by a mitral prosthesis remains an infrequent complication, perhaps because it often is unrecognized. This complication would mainly be seen with ball prostheses or standard bioprosthesis used in mitral valve replacements with a small ventricle. Two cases have been recently reported during mitral valve replacement. The two patients were successfully re-operated upon, one after five weeks and the second immediately after the first procedure. A review of the literature enable to specify the etiology and diagnostic criteria with the assistance of Doppler-sonocardiography. Early re-operation may prevent death, often due to a post-operative myocardial dysfunction.