The aim of this investigation was to compare the preventive effect of sulodexide, a glycosaminoglycan drug, tested versus ASA-dipyridamole association, on the occlusion of venous aortocoronary bypass. A group A of 23 patients, for a total of 22 anastomosis with internal mammary artery and 46 venous bypass, was treated with sulodexide 500 USL/day. A group B of 18 patients for a total of 19 anastomosis with internal mammary artery and 33 venous bypass, was treated with ASA-dipyridamole 300 mg + 400 mg/day. Three and 9 months after surgery, all patients underwent thallium-201 myocardial perfusion imaging, associated with ergometric test. At the first control after 3 months, reversible perfusion defect in one or more myocardial segments was observed in 8 patients of group A and 3 patients of group B (2 A patients and 1 B patient in non revascularized myocardial segments); after 9 months, reversible perfusion defects were observed in 4 A patients and in 4 B patients. After 3 months, non reversible perfusion defect imaging in non infarcted myocardial segments was observed in 2 A patients and in 1 B patient; after 9 months, in 1 patient of both groups. This research shows higher incidence, at first control after 3 months, of ischemic reversible perfusion defects in patients treated with sulodexide, with an evident improvement in some patients recontrolled after 9 months. At the last control after 9 months, the scintigraphic findings showed similar evidence of perfusion defects in both groups treated with sulodexide or ASA-dipyridamole, with concordant angiographic findings (78.6%). Our preliminary results are encouraging and suggest further widespread studies on sulodexide therapy.