Significant atherosclerotic changes of the coronary arteries are the common cause of cardiac chest pain. We report the case of an 80-year-old woman suffering from unstable angina caused by extracoronary atherosclerosis. The patient had an extensive medical history with severe coronary heart disease and cardiac bypass surgery (LIMA to LAD, two venous bypass grafts). An urgent coronary angiography was performed. The angiogram displayed the already known three-vessel disease, the bypass grafts were in a good functional condition. Subsequently, a stenosis of the proximal segment of the left subclavian artery was detected. Measurement of the pullback pressure gradient confirmed the significance of the stenosis. We suspected a “steal phenomenon” concerning the bypass graft LIMA to LAD. An ad hoc PTA with consecutive stenting (self-expandable stent) enabled a successful revascularization of the left subclavian artery without any adverse effects to the vertebral arteries. Cardiac chest pain did not occur any more. Coronary Subclavian Steal Syndrome should be considered a rare but important differential diagnosis in acute coronary syndrome after bypass surgery.