Abrupt closure remains a significant complication of PTCA. On the basis of the presumption of underlying cause (thrombus, dissection, spasm), various empiric medical and mechanical interventions have been used to prevent and/or treat this event. Despite these measures, however, abrupt closure remains a highly unpredictable occurrence with a substantial incidence of myocardial infarction and angioplasty-related morbidity and mortality. Direct visualization of the site of abrupt closure may allow determination of responsible mechanisms and appropriate treatment strategies. Intracoronary visualization using a new angioscope was carried out in two cases of abrupt closure after percutaneous coronary angioplasty. The angioscope features a movable fiberoptic bundle that provides continuous and uninterrupted imaging of the coronary artery segment incorporating the site of abrupt closure. In one patient with intraprocedural closure angioscopy revealed obstruction of the lumen with extruded plaque material. In a second patient with postprocedural closure, however, imaging at the site of coronary artery occlusion revealed a mass consistent with a large platelet thrombus. Intracoronary evaluation with angioscopy may yield important characteristics that identify lesions at risk for abrupt closure. Further elucidation of the mechanisms underlying abrupt closure may allow more appropriate selection of therapeutic interventions.