A Patient with a ruptured left ventricular anterior papillary muscle after acute myocardial infarction was examined by transthoracic echocardiography and transesophageal echocardiography. The patient a 69-year-old female was admitted because of severe chest pain. An emergency transthoracic two dimensional echocardiogram and color flow Doppler echocardiogram demonstrated a mobile echogenic mass attached to the tip of a mitral valve leaflet and swinging into the left atrium. Anterolateral wall akinesis and mitral regurgitation with an acceleration signal in the left ventricular chamber were also demonstrated. Using Doppler echocardiography, mitral regurgitant flow velocity of 2.5 m/sec was detected. Transesophageal echocardiography demonstrated a mobile mass attached to the chordae tendinae. A chordae attached to the head of the anterior papillary muscle flailed into the left atrium during systole. Under color flow Doppler echocardiography, severe mitral regurgitation with a large acceleration flow signal could be discerned. Transthoracic echocardiography in combination with transesophageal echocardiography is thus useful in diagnosis of a ruptured left ventricular anterior papillary muscle.