We present the case of a type AB thymoma in a 69-year-old man with previous coronary artery bypass grafting (CABG) in whom angiography revealed a left internal mammary artery graft supplying blood flow to a thymic neoplasm, which simultaneously occluded the graft. This required a redo sternotomy, lysis of pericardial adhesions, complete thymectomy, and redo one vessel off-pump CABG. This case seeks to sensitize physicians to the possibility of coronary adverse events in patients with a previous CABG in the setting of management of mediastinal neoplasms, and it presents the novel findings on cardiac imaging associated with this case.