Because of its durability and patency, the left internal mammary artery (LIMA) is preferentially used to bypass obstructive lesions in the left main coronary artery (LMCA) and/or the left anterior descending coronary artery (LAD). The long-term patency of the LIMA graft is determined by several factors, principal among them being the dynamic competition between flow through the internal mammary artery graft and the LAD. We report a patient with LMCA stenosis and a well-functioning and mature LIMA graft, who after percutaneous intervention of the LMCA and normalized antegrade flow in the LAD, developed atresia of a large caliber LIMA graft.