I have been feeling extremely lightheaded, dizzy, and feel like my heart is beating a hundred miles per hour. only happens when i drive why?

Unusual Problem: The clue that the symptoms occur only when driving suggest a connection to arm exercise. This can be a result of "subclavian steal, " a condition in which a narrowed artery in the shoulder results in blood for the arm being diverted from the brain. A careful examination and ultrasound testing may reveal this diagnosis which is confirmed by angiography and is curable by stenting.