Definition of Subclavian steal

Subclavian steal: The symptoms of cerebral vascular insufficiency (not enough blood to the brain) when the patient exercises an arm, due to obstruction of the subclavian artery before the origin (the takeoff) of the vertebral artery. Exercising the arm causes the blood flow to reverse and the subclavian artery "steals" blood from the vertebral artery. The subclavian normally supplies blood to the arm while the vertebral artery conveys blood to the brain, so what is happening in the subclavian steal is that blood meant for the brain is stolen by the arm.