Left ventricular wall motion abnormalities, the extent and location of coronary artery stenoses, and the radiographic evidence of pulmonary venous hypertension were analyzed in a retrospective study of 40 patients who had surgically proven rupture of the interventricular septum after myocardial infarction. In 33 patients in whom chest films were available, interstitial or alveolar pulmonary edema was present in 78%, while left ventricular enlargement was present in 82%. Of 26 patients who had coronary angiography, complete occlusion of the right coronary artery, left anterior descending artery, or left circumflex artery was present in 92%, with few, if any, collateral vessels around the occlusion. The location of the rupture in the muscular septum was always in the region of akinesis or dyskinesis. Posterior defects were associated with posterobasal and diaphragmatic akinesis, and anterior defects with apical akinesis. Left ventricular aneurysms were adjacent to the septal rupture in 68%, and 74% had mitral regurgitation. The right ventricular diaphragmatic wall in posterior rupture was always akinetic, indicating right ventricular infarction. Thus ventricular septal defect after myocardial infarction (1) tends to occur with multiple coronary occlusions about which little collateral flow develops; (2) can accurately be localized anteriorly or posteriorly in the muscular septum by the location of the akinetic left ventricular wall segment; and (3) has an associated right ventricular infarct when rupture is posterior.