Patients with less severe atherosclerosis (insignificant CAD and single-vessel disease) who experienced combined cardiac adverse events exhibited lower baseline kynurenine levels and IDO activity than those who had no events (0.38 vs. 4.94, p = 0.017; and, 0.01 vs. 0.14, p = 0.023, respectively). Here, IDO1 is linked to coronary artery disorder.