Background: CD147, also known as extracellular matrix metalloproteinase inducer, is present on circulating platelets and leukocytes in patients with coronary disease and is implicated in atherogenesis, and plaque rupture. We investigated whether CD147 (platelet, leukocyte and soluble) is upregulated within the coronary circulation in patients with stable coronary disease, and whether CD147 levels are associated with coronary shear stress levels. Methods: A total of 25 patients undergoing intervention of a single coronary lesion had blood sampled within the coronary (n=15) and peripheral circulation (n=10). Platelet and leukocyte CD147 expression was measured by flow cytometry. Soluble CD147 was measured by enzyme-linked immunosorbent assays. Shear stress was calculated using computational fluid dynamics analysis. The effect of shear on platelet CD147 expression in vitro was investigated using a cone-plate viscometer. Results: Platelet CD147 was higher in the coronary sinus (CS) compared to femoral vein (mean±SD fluorescence intensity: 3.1±0.7 vs. 2.2±0.5, p=0.01). There was a significant linear trend for increased platelet CD147 expression from the proximal artery to the distal artery, and subsequently to the CS (p=0.01), indicating trans-lesion and transmyocardial upregulation. There were no differences between the various sites for monocyte, granulocyte or soluble CD147 levels (all p=ns). Trans-lesion gradients of CD147 did not correlate with shear stress (all p=ns). Blood subjected to shear in vitro had higher levels of platelet P-selectin (p=0.04) but similar levels of platelet CD147 (p=0.46) compared to rested blood. Conclusion: Platelet CD147 expression is upregulated in the coronary circulation in patients with stable coronary disease, but its upregulation is independent of shear stress.