Objectives. The aim of this study is to compare the endothelial integrity of saphenous vein grafts harvested by minimally invasive surgery and veins harvested conventionally for coronary artery bypass surgery in 200 participants who were assigned to interventions by using random allocation. Design. Randomized controlled trial. Methods. Immunocytochemistry with anti-CD 31 antibodies and anti-nitric oxide synthase (NOS) antibodies were employed to identify the endothelial integrity. Results. The CD 31 immunostaining showed that the endothelial cell integrity of the minimally invasive harvested veins was preserved in 82^13% of the circumference of luminal endothelium, while in conventionally harvested grafts it was reduced to 64^15% (p ¼ 0.05).> This was associated with the lack of CD 31 expression in vasa vasorum (10 and 18%) in both groups, respectively, (p ¼ 0.02). The NOS immunostaining revealed that the endothelial integrity of the minimally invasive harvested grafts was preserved in 96^4% of the luminal endothelium circumference as compared to 74^10% in conventionally harvested grafts (p ¼ 0.05). The percentage of cases with the lack of NOS expression in all vasa vasorum was 12 and 21%, in G1 and G2, respectively, (p ¼ 0.02). Conclusion.The endothelial integrity of saphenous vein grafts harvested by minimally invasive surgery is better preserved than with the grafts obtained by the conventional manner. This could play an important role in improving vein graft patency rates.