A case of acute severe mitral regurgitation with serious hemodynamic impairment in the setting of an inferior ST-elevation myocardial infarction is presented. Both transthoracic and transesophageal echocardiography demonstrated a posteriorly directed eccentric jet of severe mitral regurgitation with flail anterior mitral valve leaflet. The rupture of the postero-medial papillary muscle attached via chords to the anterior mitral valve leaflet was found. The direction and eccentricity of the mitral regurgitant jet on transthorasic and transesophageal echocardiography helped to point the leaflet involved, but not necessarily the coexisting papillary muscle pathology.