The vertebral arteries, at the base of the neck, deliver oxygenated blood to the brain. These arteries branch off into the arms forming the subclavian arteriers. These two subclavian arteries are the primary suppliers of blood to the arms.

Dizziness can occur when the arm takes a larger proportion of blood from the brain, creating a blockage. Diagnosed fairly easy when blood pressure differs in each arm, most patients assume it is just fatigue. Vascular surgeons treat this problem with angioplasty or bypass.