Antiplatelet therapy is critical in the management of coronary artery disease.For patients undergoing off-pump coronary artery bypass graft,controversy remains regarding the safety of preoperative antiplatelet therapy.And there is little study about the effect of continuing aspirin until the surgery day on graft patency.So we would like to perform this study to evaluate the effects of preoperative aspirin on graft patency and cardiac events in off-pump coronary bypass.

Inclusion Criteria:

• Patients undergoing elective, off-pump coronary artery bypass with at least two grafts
• patient able to give informed consent

Exclusion Criteria:

• on-pump CABG
• combined with the valve surgery
• Preoperative use of clopidogrel and warfarin
• allergy to aspirin
• History of severe liver disease
• History of bleeding diathesis,significant GI bleed
• Patient has known renal failure or contraindication for Cardiac CT Angio
• Redo CABG