Differences in morphological characteristics have been described in early phase and late phase post-infarction cardiac rupture. In this study, the clinicopathological characteristics of early and late phase rupture have been clarified by reviewing the clinical records of 1450 consecutive patients with acute myocardial infarction (AMI). Rupture of the left ventricular free wall (blow-out type) developed in 27 of the 1450 patients, and these patients were divided into two groups on the basis of the rupture time: early phase (< 72 h) and late phase (> 4 days). Only one patient had a history of prior infarction. Early phase rupture was characterized by an abrupt slit-like tear in the infarcted myocardium, a preference for anterior infarction sites, no prior myocardial infarction, and no difference in incidence in conventional and reperfusion therapy, while late phase rupture was characterized by the presence of infarct expansion, no preferential infarct site and a very low incidence in patients with successful reperfusion. Hence, early and late phase cardiac rupture differ in their pathogenesis, and thus the approach to the prevention and prediction of early and late phase cardiac rupture should be different.