It has been shown that localized myocardial ischemia is accompanied by microvascular changes which produce capillary obstruction when blood flow is restored. This so-called no-reflow phenomenon has been noted in the brain, kidney, dermis and more recently, in the myocardium. Ultrastructural studies have pointed out the role of myocardial and endothelial cells'' swelling. Such damage of the vascular bed may constitute the 1st irreversible change during ischemia and result in failure to obtain successful re-perfusion of involved myocardium. This phenomenon may play a role in subendocardial necrosis associated with [human] cardiac surgery, and in myocytolytic necrosis. In both of these conditions, the most salient features are the microcirculatory defect and the re-perfusion injury following transient ischemia.