The right gastroepiploic artery (RGEA) has been used in coronary artery bypass grafting (CABG) as an alternative graft. In particular abdominal surgeries, surgery is required to rescue the graft flow into the coronary artery. A 77-year-old male with a history of CABG using RGEA was admitted with a diagnosis of a large hepatocellular carcinoma (HCC) occupying the whole caudate lobe. Preoperative coronary angiography indicated that the graft from the right internal mammary artery to the proximal left circumflex artery was obliterated among three branch bypasses. Following laparotomy, a great saphenous vein was harvested and delivered from the right axial artery to the RGEA graft over the thoracic wall, and the RGEA graft was ligated and divided. Subsequently, extended left hepatectomy was safely performed. Following hepatectomy, the RGEA graft was restored to the former condition, and the temporary graft was removed. After overcoming hyperbilirubinemia, the patient was discharged on postoperative day 28. This experience indicates that temporary bypass using the long great saphenous vein is effective and safe during long and invasive surgeries.