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James Richard Spears Cardiovascular Research Laboratory, Department of Medicine, Division of Cardiology, Beaumont Heart & Vascular Center, Dearborn, MI 48124, USACorrespondence: James Richard SpearsCardiovascular Research Laboratory, Department of Medicine, Division of Cardiology, Beaumont Heart & Vascular Center, 22060 Beech St, Suite 200, Dearborn, MI 48124, USATel +1 313-228-0505Fax +1 313-228-0508Email james.spears@beaumont.orgAbstract: Following a prolonged coronary arterial occlusion, heterogeneously scattered, focal regions of low erythrocyte flow are commonly found throughout the reperfused myocardium. Experimental studies have also demonstrated the presence of widespread, focally patchy regions of microvascular ischemia during reperfusion (RMI). However, the potential contribution of RMI to tissue viability and function has received little attention in the absence of practical clinical methods for its detection. In this review, the anatomic/functional basis of RMI is summarized, along with the evidence for its presence in reperfused myocardium. Advances in microcirculation research related to obstructive responses of vascular endothelial cells and blood elements to the effects of hypoxia and low shear stress are discussed, and a potential cycle of intensification of RMI from such responses and progressive loss of functional capillary density is presented. In capillaries with impaired erythrocyte flow, compensatory increases in the delivery of oxygen, because of its low solubility in plasma, are effective only at high partial pressures. As discussed herein, attenuation of the cycle with oxygen at hyperbaric levels in plasma is, very likely, responsible for improved tissue level perfusion noted experimentally. Observed clinical benefits from intracoronary SuperSaturated oxygen (SSO2) delivery, including infarct size reduction, can be attributed to attenuation of RMI with improvement in microvascular blood flow.Keywords: oxygen, ischemia, capillaries, reperfusion, plasma