Plasma venous samples will be collected the day before surgery, at discharge from the hospital, and at follow-up from patients undergoing on-pump and off-pump coronary artery bypass grafting and stored at -80°C; Patients will be followed-up periodically with visits and telephone interviews, and will be also invited to undergo multislice (64 rows) CT scan in order to assess graft patency between 12 and 24 months after surgery.