Ten dogs underwent coronary artery bypass grafting through a right thoracotomy. Free internal mammary artery grafts (IMA) was used for aortocoronary bypass to right coronary artery (RCA) without temporary cardiopulmonary bypass. In upper median laparotomy approach, mobilization and lengthening of the omentum was performed through the retrosternal part of the diaphragm. An epiploic muff was effectuated surrounding the IMA graft. After three months the animals were sacrificed and the grafts folded by omentum were used for microscopical study. The histological evaluation has shown that the omentum has formed a new adventitia around the graft. In the new-formed adventitia, newly formed vessels can be found and these are grouped around the adventitia-media border zone, very rarely penetrating into the external layer of the media. This graft-omentoplasty offer a good experimental model which facilitates to investigate in vivo the blood supply needed by free IMA grafts through the adventitia in experimental conditions. The biological mechanism of angiogenesis in graft wall can be investigate as well.