Background: In some patients with papillary muscle rupture, the ruptured head may not prolapse into the left atrium, which makes diagnosis by transthoracic or transesophageal echocardiography difficult. Methods and Results: In an attempt to find additional or more definite diagnostic echocardiographic features, we analyzed intraoperative transesophageal echocardiograms of 21 consecutive patients with papillary muscle rupture (20 involved the left ventricle and 1 involved the right ventricle) confirmed at surgery. In 7 (35%) of 20 patients with left ventricular papillary muscle rupture, the ruptured head was not seen to prolapse into the left atrium. In these patients, examination of the left ventricle proved most useful. Abnormal, large-amplitude erratic motion (1 to 5 cm in 17 patients; 0.5 cm in 1 patient) of a large echo density in the left ventricle consistent with the ruptured head was noted in 18 (90%) of these 20 patients. This included all 7 patients with non-prolapse of the ruptured papillary muscle head into the left atrium. Less prominent erratic motion or flutter of the papillary muscle still attached to the left ventricular wall was also noted but was less sensitive in the diagnosis of papillary muscle rupture. The single patient with right ventricular papillary muscle rapture showed erratic motion as well as prolapse of the ruptured head into the right atrium. Conclusions: Transesophageal echocardiographic examination of the left ventricle is useful in the diagnosis of papillary muscle rupture, especially in those patients in whom the ruptured head does not prolapse into the left atrium. The left ventricle should be scrutinized thoroughly during transesophageal echocardiographic examination for erratic papillary muscle motion in all patients with suspected rupture.