SUMMARY We quantitated hemorrhage associated with reperfusion after varying periods of myocardial ischemia and examined the flow characteristics that accompany reperfusion hemorrhage. Anesthetized dogs were reperfused after 2, 6 or 24 hours of circumflex occlusion. A control group underwent coronary occlusion without reperfusion. Radioactive microspheres were injected before and 5 minutes and 24 hours after reperfusion. The papillary muscles were analyzed for hemoglobin content, flow during myocardial ischemia and flow early and 24 hours after reperfusion. Myocardial creatine kinase activity was assayed to determine the severity of myocardial necrosis in the papillary muscles.Hemorrhage into the posterior papillary muscle was dependent upon the duration of coronary artery occlusion. Posterior papillary hemoglobin averaged 14 mglg in the 2-hour group, 28 mg/g in the 6-hour group and 36 mg/g in the group reperfused 24 hours after occlusion, compared with 8.7 mg/g in the control group. Myocardial hemorrhage was associated with severe depression in myocardial CK and marked depression in flow to the ischemic area (i.e., collateral flow) during the occlusion. Early reflow averaged 112 ml/min/100 g in the 2-hour group, 61 ml/min/100 g in the 6-hour group and only 5.8 ml/min/lO0 g in the 24-hour group. Therefore, myocardial hemorrhage induced by reperfusion of the acutel ischemic myocardium is associated with severe ischemia during occlusion and severe myocardial necrosis, but does not depend upon the magnitude of early reflow. Myocardial hemorrhage may occur even though initial reflow values are markedly decreased.REPERFUSION of the acutely ischemic myocardium might appear to be an easy way of reversing myocardial ischemia and limiting the eventual extent of myocardial infarction. Reperfusion after brief periods of myocardial ischemia does prevent the development of infarction, and reperfusion after 3 hours of myocardial ischemia may limit the eventual infarct size.'4 The benefits of reperfusion, however, are controversial.Some studies have demonstrated an exacerbation of ventricular arrhythmias, accelerated morphologic changes of ischemia and worsening metabolic function.5-10 The deleterious effects of reperfusion are often associated with myocardial hemorrhage.45' 7 9 This supposedly occurs because of irreversible damage to the microcirculation and the extravasation of blood on reperfusion. Hemorrhage on reperfusion has also been described in man, particularly after long periods of intraoperative myocardial ischemia. Coronary artery bypass surgery in the setting of acute myocardial infarction is being performed more and more frequently and streptokinase-induced reperfusion is receiving widespread acceptance."-14 Thus, reperfusion in the setting of myocardial infarction is a clinical reality and broader knowledge is required about the phenomenon of hemorrhage upon reperfusion.Accordingly, we examined the phenomenon of myocardial hemorrhage upon reperfusion of the acutely ischemic myocardium. We studied the frequency o...