Question

why are value present in heart and veins

Answer 1

valves r present to prevent the backflow of blood

Answer 2

heya,

here is ur answer

veins are present in the heart in order to transport the blood to different parts. and different valves contains different veins.
these valves are used for getting the blood from other parts which is deoxyginated which is less of O2 and the others two valves are fro sending the blood to different parts which is oxygenated with O2 there are two valves two for deoxyginated and two for oxygenated
valves are also present for to prevent the backflow of the blood.

hope this helps u
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sid071