Left ventricular pseudoaneurysms are an uncommon and frightening complication after mitral valve replacement. We report the case of a 54-year old woman, having undergone a mitral valve replacement with uneventful postoperative course and normal echocardiographic predischarge control, who was readmitted to hospital, only 16 days later, for rapidly progressing dyspnea, and finally echocardiographically diagnosed to have a massive 8-cm long pseudoaneurysm communicating with the left ventricle through a narrow communication. The patient was proposed for emergency surgery but unfortunately died preoperatively.