In coronary artery bypass grafting, saphenous veins are widely used as a composite grafts that are Y-anastomosed to in-situ left internal thoracic artery. Based on our observation that remodeling of saphenous vein graft differs between those harvested from upper leg vein and lower leg, this study aims to compare histologic and immunohistochemical findings between saphenous vein grafts harvested from upper leg and lower leg.

Inclusion criteria:

• Patients aged from 40 to 75 years with triple vessel disease
• Patients who are eligible for the use of left internal thoracic artery as an in situ primary conduit
• Operation plan: saphenous vein graft will be Y-anastomosed to left internal thoracic artery.
• Patients whose saphenous vein grafts can be harvested from both upper legs and lower legs
• Patients who are eligible for off-pump coronary artery bypass grafting
• Patients who agreed with the participation in the research based on thorough explanation.

Patients will be randomly assigned to upper leg vein (ULV) group and lower leg vein (LLV) group immediately after anesthetic induction.

Pieces of residual saphenous vein graft will be sent for histologic and immunohistochemical examination for the evaluation of endothelial cell preservation and the expression of matrix proteins.

Inclusion Criteria:

• Patients with multivessel disease who were planned to undergo off-pump coronary artery bypass grafting
• Patients whose left internal thoracic arteries can be used, and whose saphenous vein grafts will be Y-anastomosed to left internal thoracic arteries.
• Patients whose saphenous vein grafts can be harvested from both upper and lower legs.

Exclusion Criteria:

• Patients with overt heart failure symptoms
• Patients with intractable ventricular arrhythmia
• Patients with history of cancer or malignancy
• Patients with coagulation or other hematologic disorder
• Patients who needs concomitant cardiac procedures