Question

why are the valves needed in the heart

Answer 1

it is to make sure that blood flows only in one direction

Answer 2

The valves are present in the heart to prevent the back flow of blood.

The flow of the oxygenated and the deoxygenated blood should always be in only one direction so as to formulate their destinations, the oxygenated blood can be directionally maintained because of the enormous amount of pressure that builds up in the vessels due to the pumping of the heart, whereas the deoxygenated blood do not have such pressure inbuilt in them.