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Vicken Zeitjian,1 Carmel Moazez,1 Mehrdad Saririan,2 David L August,3 Ranjini Roy2 1Department of Internal Medicine, 2Department of Cardiology, 3Department of Radiology, Maricopa Integrated Health System, Phoenix, AZ, USA Introduction: Anomalous origin of the right coronary artery (RCA) from the left coronary cusp of the aorta is a moderately rare but potentially life-threatening incident. Myocardial infarction (MI) and sudden cardiac death have been described with this anomaly, especially in those who engage in excessive exercise. However, this case study shows this incidence in association with hyperthyroidism.Case description: A previously healthy 51-year-old female with history of hypothyroidism presented with acute onset chest pain for 1 day. Patient’s electrocardiogram was normal, however, she had elevated troponins and given her typical chest pain, she was diagnosed with acute coronary syndrome (ACS). The patient had been on levothyroxine and was found to have a subnormal thyroid-stimulating hormone level suggesting hyperthyroidism. Echocardiogram was normal. Coronary angiogram showed an anomalous RCA arising from the left coronary cusp of the sinus of Valsalva and no evidence of atherosclerosis. A coronary computed tomography angiogram was done confirming this finding and showed a slit-like deformity of the coronary ostium with at least 50% luminal stenosis. The patient was referred to a cardiothoracic surgeon for potential coronary artery bypass graft.Discussion: This case illustrates a rare presentation of ACS due to hyperthyroidism in an anomalous RCA. MI is a rare manifestation of hyperthyroidism, but in combination with an anatomical defect, it can potentiate adverse outcomes. The mechanisms by which thyroid hormones influence cardiovascular hemodynamics are by causing a hyperdynamic circulatory state, increasing myocardial oxygen demand, and increasing the risk of coronary vasospasm. The combination of anatomic and metabolic defects is what likely precipitated this patient’s outcome. Keywords: hyperthyroidism, anomalous coronary artery, acute coronary syndrome, risk factors for acute coronary syndrome