Background. Patent bypass grafts are fundamental to successful coronary artery bypass grafting. Intraoperative flow measurement through newly constructed grafts is a test of patency. We studied the use of transit-time flow measurement to determine its ability to detect technical errors in grafts, to measure the mean flow norms, and to compare flow in on-pump and off-pump CABG procedures.Methods. From December 2001, to December 2004, 40 patients underwent isolated primary coronary artery bypass grafting. Twenty patients underwent conventional coronary artery bypass grafting and twenty patients underwent off-pump coronary artery bypass grafting. There were 54 arterial and 47 vein grafts. Transit-time flow measurement was carried out on all completed grafts. Graft patency was assessed using flow curves, mean flow, and pulsatility index. Average of mean flows was calculated to determine mean flow norms. Arterialand vein grafts were compared by statistical analysis between the variables mean flow and pulsatility index.Results. 2/52 (3.8 %) of the grafts in group A were considered “not well-functioning” and needed surgical revision; compared to 4/49 (8.1 %) of grafts in group B (p < 0.001). In the conventional group A, two SVGs: one to the diagonal (intimal flap) and one to the OM2 branch (malpositioned stitch) were not well-functioning; versus 2 RA grafts: one to crux and one to PDA branch (graft stenosis), and 2 SVGs grafts: one to crux (malpositioned stitch) and one to PDA branch (dissection) in the OPCABG group.Conclusions. Transit-time flow measurement enables technical problems to be diagnosed accurately, allowing prompt revision of grafts. It should be mandatory in coronary artery bypass grafting to improve surgical outcomes.