This prospective study investigates microscopic changes in the outer layer (adventitia) of the ascending aorta in patients undergoing coronary artery bypass grafting (CABG) surgery. The study includes two groups of patients: (1) those with borderline ascending aortic dilatation (4.0-5.0 cm), and (2) a control group with normal aortic diameter (<4.0 cm), all undergoing the same surgical procedure. During CABG, a small circular punch is routinely made in the ascending aorta for the proximal saphenous vein graft anastomosis. The tissue removed from this punch site is collected and used for histopathological and immunohistochemical analysis. The study aims to determine whether adventitial changes correlate with aortic size and whether these changes can help identify patients at risk for future aortic dissection or rupture. The findings may guide surgical decision-making in patients with borderline aortic enlargement.

Inclusion Criteria:

1. Adults aged between 20 and 70 years

2. Patients scheduled for elective open-heart coronary artery bypass grafting (CABG)

3. Patients undergoing their first cardiac surgery

4. Metabolically stable patients

5. Aortic diameter:

   1. Observational aortic dilatation group: between 4.0 cm and 5.0 cm
   2. Control group: less than 4.0 cm

6. Written informed consent obtained from the patient

Exclusion Criteria:

1. History of previous cardiac surgery
2. History of aortic dissection or rupture
3. Known genetic syndromes (e.g., Marfan, Loeys-Dietz, Ehlers-Danlos)
4. Known systemic vasculitis
5. Presence of acute infection or systemic inflammatory disease
6. Inadequate biopsy material for pathological analysis
7. Patients not undergoing any aortic intervention during surgery

The study population includes adult patients aged 20 to 70 years undergoing elective coronary artery bypass grafting (CABG) surgery at a tertiary cardiovascular surgery center. Participants are divided into two groups based on preoperative ascending aortic diameter measured by imaging:

Study Group: Patients with borderline ascending aortic dilatation (diameter between 4.0 cm and 5.0 cm) Control Group: Patients with normal ascending aortic diameter (<4.0 cm) All participants are undergoing their first cardiac surgery, are metabolically stable, and do not have a known history of aortic dissection, connective tissue disease, or systemic vasculitis.