Background; Several previous studies suggested long term endothelium related vascular dysfunction after drug eluting stent (DES) by various invasive methods. Purpose; This study was designed to investigate whether endothelial dysfunction is related to DES implantation at long term after DES deployment by noninvasive assessment of coronary flow reserve (CFR) in the left anterior descending artery (LAD) by transthoracic echocardiography. Method; 91 patients (mean age, 59.7짹9.6, male 71.4%) were selected from a population undergoing diagnostic or follow up (mean duration; 9.7짹2.5months) coronary angiography. The requisite to be enrolled this study was the presence of angiographically looks normal LAD with or without previous history of LAD stenting. 69 patients who received percutaneous coronary intervention with DES due to coronary arterial disease (LAD stenting group (n=56); non LAD stenting group (n=13)) and 22 controls without angiographically detectable lesion were included in this study. We estimated endothelial function by transthoracic assessment of CFR with adenosine induced hyperemia. Result; All patients of control group and non-LAD group showed preserved endothelial function (CFR>2), but in LAD stenting group, 21 patients (37.5%) showed endothelial dysfunction (CFR ��� 2) (p=0.002). The CFR value of LAD stenting group showed significantly decreased compared to normal control group and non-LAD stenting group, and that of non-LAD group also showed significant decreased CFR value compared to control group. Conclusion; This study demonstrated that endothelial dysfunction long after DES deployment despite of angiographically normal finding.