Background: We investigated in a porcine model whether measuring both the flow distal to an anastomosis and the graft transit time flow (TTF) gives a more accurate picture of the true blood flow in the left anterior descending artery (LAD) than graft TTF measurement alone.Methods: We performed off-pump coronary artery bypass grafting (CABG)-left internal mammary artery (LIMA) to the LAD-on 5 Yorkshire-Landrace pigs. Snares were placed both proximal and distal to the anastomosis. Flow was measured with ultrasound and TTF. This was carried out on the LIMA and at 2 locations on the LAD. Measurements were performed at the following times: baseline, during proximal snaring, after proximal snare loosening, during distal snaring, after distal snare loosening, and during both proximal and distal snaring.Results: During distal snaring, the TTF dropped (P = .047), and the pulsatile index (PI) increased (P = .025), while the ultrasound flow in the LAD dropped (P = .002). During proximal and distal snaring, the ultrasound flow dropped (P = .005), but the TTF value did not change significantly, compared with baseline.Conclusion: A high flow and a low PI were seen in the graft, both proximal and distal to the anastomosis, despite a fully occluded LAD. This result suggests that graft TTF measurement alone is not sufficient when performing CABG, and measurement of flow distal to the anastomosis is also necessary to determine the true blood flow in the LAD.