Optical coherence tomography (OCT) has been recently studied for evaluation of coronary stenting. Because of high resolutions, several reports have shown that OCT is appropriate for evaluating neointimal tissue after coronary stent implantation. Also, the strut coverage and the characterization of neointimal tissue can be accurately evaluated. Furthermore, OCT-defined coverage of a stent strut was proposed to be related with clinical safety in drug-eluting stents-treated patients. Therefore, the investigators will evaluate the appropriateness of currently using coronary stents (e.g. Sirolimus eluting stent, Paclitaxel-eluting stent, Zotarolimus-eluting stent, Everolimus-eluting stent, Biolimus eluting stent, EPC(endothelial progenitor cell) Capture stent, etc) based on the findings of OCT. Additionally, the investigators will evaluate neointimal hyperplasia, malposition or strut coverage to decide the differences in the stent characteristics, the duration of antiplatelet use, and the differences according to the clinical presentations.

Inclusion Criteria:

1. Patients with coronary stents
2. Patients who will have coronary stents because of coronary artery stenosis

Exclusion Criteria:

1. Hemodynamically unstable patients
2. Ostial lesions that begin within 15 mm of the left main coronary artery
3. Lesions with diameter more than 4 mm
4. Patients with allergy to antiplatelet agent (asprin or clopidogrel)
5. Patients with hepatic dysfunction (Liver enzyme 3 times the upper limit of normal)
6. Pregnant and lactating patients
7. Patients with life expectancy less than 1 year

Patients who visited our tertiary hostpital (Severance Cardiovascular Hospital) for coronary angiography (with coronary stents or planning for coronary stents)