Abstract. A 61-year-old diabetic woman was referred for myocardial perfusion single photon emission computed tomographic (SPECT) imaging 4 years after coronary artery bypass grafting to the left anterior descending (LAD) artery using a left internal mammary artery (LIMA) graft. She had 3 months’ angina associated with fatigue of her left upper extremity (the patient is left-handed). Stress myocardial imaging using a Bruce protocol did not exhibit significant myocardial ischemia, but because of her typical angina symptoms, she underwent repeat stress myocardial imaging in combination with exercise of her left arm. During the aforementioned modified stress protocol, the patient reported angina, and radionuclide perfusion imaging showed extensive myocardial ischemia. The patient underwent coronary angiography and arteriography of the left subclavian artery, which revealed severe stenosis before the origin of the LIMA, resulting in reversed blood flow from the LAD artery through the LIMA graft to the left subclavian artery.