The angiographic and pathologic findings are described in three patients who died less than 24 h after failed percutaneous transluminal coronary angioplasty. In two of the three patients, coronary angiography performed before angioplasty disclosed apparently focal lesions in the left anterior descending and right coronary arteries. In these two patients quantitative angiographic analysis disclosed a minimal lumen cross-sectional area of 1.82 and 0.47 mm2, respectively, at the sites of apparently focal stenoses before angioplasty; corresponding percent lumen area narrowing measured 84% and 91%, respectively, by quantitative angiography at these two sites. In the third patient, coronary angioplasty was undertaken when the patient developed spontaneous occlusion of the right coronary artery several hours after diagnostic angiography. Retrospective quantitative angiographic analysis of the right coronary artery revealed a minimal lumen cross-sectional area of 1.14 mm2, with 85% lumen area narrowing at the site of subsequent total occlusion and angioplasty. In each of these three patients, necropsy examination disclosed that the distribution of coronary narrowing in the artery treated by angioplasty was in fact not focal; rather, in each of these three patients, the artery treated by angioplasty, as well as the extramural coronary arteries not treated by angioplasty, were severely narrowed by diffusely distributed atherosclerotic plaque. The angiographic and necropsy findings in these three patients document that coronary narrowing that remains occult by virtue of diffuse distribution may complicate evaluation of patients being considered for coronary angioplasty.