Background: Recent several studies have showed that stromal cell derived factor-1 (SDF-1), originally known as a cytokine in recruiting stem cells into injured organs, confers myocardial protection in myocardial infarction, which is not dependent of stem cell recruitments but related with modulation of mechanism of ischemia reperfusion injury (I/R injury). However, the effect of SDF has been studied only in model of preischemic exposure, which is not clinically relevant if SDF is to be used as therapeutic agent. Objective : Our study was to evaluate whether or not the SDF-1 confers cardioprotection during reperfusion period. Methods : Hearts from SD rats were isolated and perfused with Langendorff system. Proximal LAD ligation and reperfusion was made according to study protocol (figure). SDF was infused through KH buffer according to study protocol. Area of necrosis (AN) out of area of ischemia (AR, area of risk) was primary endpoint of each group. Results: Significant reduction of AN/AR by SDF was noted both in pre-ischemic exposure and during reperfusion periods (figure). In groups of SDF during reperfusion, it appreas to have a trend of dose dependent response. Especially, high concentration of SDF(25nM/L) infusion results in such a dramatic reduce of infarct size that its infarct reduction effect exceeded the results of ischemic pre or post conditioning. Conclusion : Intracoroanry infusion of SDF during reperfusion showed significant reduction of infarct size like preischemic SDF exposure. This result may call for further studies to find the potential possibility of SDF as a therapeutic agent for reducing IR injury in clinical practice.