Purpose:　The　internal　thoracic　artery　is　the　choice　of　graft　for　coronary　artery　bypass　grafting　due　to　the　excellent　long-term　patency.　However　internal　thoracic　artery　graft　failures　still　occur　due　to　diffuse　narrowing,　known　as　the　string　phenomenon.　Studies　suggest　that　the　string　phenomenon　is　caused　by　competitive　flow　when　the　coronary　stenosis　is　not　serious,　but　the　hemodynamics　of　the　string　phenomenon　are　still　unclear.　The　purpose　of　this　study　is　to　clarify　the　hemodynamic　characteristics　of　the　string　phenomenon.　Materials:　A　patient-specific　3-dimensional　model　of　the　aortic　arch　and　coronary　arteries　was　reconstructed.　A　moderate　stenosis　was　applied　to　the　left　anterior　descending　artery.　The　internal　thoracic　artery　was　used　to　bypass　the　stenosis.　Two　further　3D　models　were　built　to　study　the　hemodynamics　of　the　string　phenomenon.　Methods:　A　numerical　study　was　performed　by　coupling　the　3D　artery　model　with　0-dimensional　lumped　parameter　model　of　the　cardiovascular　system.　Results:　The　graft　flow,　native　coronary　flow,　wall　shear　stress　and　oscillatory　shear　index　were　calculated　and　illustrated.　Inverse　flow　and　high　oscillatory　shear　index　appeared　on　the　internal　thoracic　artery　graft　when　the　stenosis　was　moderate.　Conclusion:　High　oscillatory　shear　index　might　be　the　major　hemodynamic　characteristic　of　the　string　phenomenon　in　internal　thoracic　artery　graft.　The　inverse　graft　flow　and,the　difference　in　graft　flow　caused　by　clamping　the　stenosis　can　be　used　to　evaluate　the　probability　of　observing　the　string　phenomenon.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.