The body is like an
orchestra, all the parts work in concert.
At some point in history the heart
was seen to be the main part, at others the brain
was viewed this way. Many organs are duplicated in case we loose one, e.g., the eyes, ears, kidneys, etc. Philosophically, the human will, choice,spirit, can be seen as the main part. Your value system will determine it for you. Peace and good health.