Seventeen of 31 patients with papillary muscle rupture (PMR) were admitted with a >24-hour delay since onset of acute myocardial infarction (AMI) in contrast to 81 of 1,012 with AMI without cardiac rupture; in 8 of 11 patients with in-hospital PMR it was preceded by new anginal pain in 5 and/or by strenuous exercise in 4; mortality was higher in those with anterior PMR, previous infarction, or 3-vessel disease than in those without PMR. Thus, persistence of physical activity before or during hospitalization, as well as postinfarction ischemia/infarct extension, appear to be relevant triggers of PMR, whereas mortality is more often associated with existence of a previous infarction, 3-vessel disease, and/or anterior PMR.