Please note that both heart and brain have a relation since brain is a control panel that manages the organs of the body and even a heart cannot function without the brain.

The heart pumps oxygenated blood into the body so that musceles and cells could recieve oxygen through this blood and after that blood flows through the entire body donating great amount of oxygen to the musceles of the body, the de-oxygenated blood then passes across the lungs recieving fresh oxygen and after returning to heart it is again pumped to the entire body.
This entire process is controlled by the brain.

It functions just like a battery where its negative and positive terminals are connected with a copper wire and a bulb is attached with it.
The electrons from the negative terminal of the battery are attracted to the positive terminal causing a flow of electrons and the bulb recieving the electrical energy from the electron uses it operate itself and these same electrons return to the battery through positive terminal and regain electrical energy from the battery and continue to flow in the wire and provide energy to the bulb.

The electrons in this case is blood and bulb in this case is the organ.

I hope you understand what I mean.

Neither heart is useful without brain nor brain is useful without heart.