Right-sided aortic arch with an isolated left subclavian artery is a very rare congenital anatomical variant that can lead to subclavian steal syndrome. We present a case of an asymptomatic patient who was incidentally found to have this variant on CT angiography with QMRA evidence of retrograde flow in the left vertebral artery consistent with subclavian steal phenomena. Since patients often remain asymptomatic until their compensatory mechanisms become compromised later in life, serial monitoring using non-invasive hemodynamic studies such as QMRA may guide treatment.