Blood　is　lost　in　coronary　artery　aneurysm　(CAA),　leading　to　a　decrease　in　downstream　blood　flow,　called　the　＂blood　stolen＂　phenomenon.　In　the　clinic,　the　＂blood　stolen＂　phenomenon　may　lead　to　dilated　myocardial　ischemia.　The　mechanism　of　dilated　myocardial　ischemia,　which　is　different　from　that　of　stenotic　myocardial　ischemia,　has　not　yet　been　studied.　The　purpose　of　this　study　is　to　reveal　the　mechanism　of　dilated　myocardial　ischemia　induced　by　the　＂blood　stolen＂　phenomenon.　In　this　paper,　a　lumped　parameter　model　of　the　cardiovascular　system　with　a　CAA　was　established,　a　parallel　structure　was　used　to　represent　CAA.　Three　different　sized　CAAs　were　simulated,　and　their　upstream　and　downstream　blood　flows　were　observed.　The　results　showed　that　small　and　medium　CAAs　lead　to　5.21%　and　9.57%　reductions,　respectively,　in　the　downstream　flow.　Giant　CAAs　lead　to　a　more　than　14%　reduction　in　the　downstream　flow,　while　the　upstream　blood　flow　showed　diastolic　backward　flow.　The　results　of　this　numerical　simulation　are　consistent　with　the　clinical　description.　When　blood　flows　into　CAAs,　it　cannot　flow　downstream　normally,　and　due　to　the　wall　elasticity　of　the　CAA,　there　is　diastolic　backward　flow,　eventually　leading　to　dilated　myocardial　ischemia.　With　expansion　of　the　CAA,　the　＂blood　stolen＂　phenomenon　will　be　more　severe.