Question

Why is it necessary to separate the left and right side of heart in mammals?

Answer 1

to avoid the mixing of oxygen rich blood and carbon dioxide rich blood
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Answer 2

Birds (some dinosaurs) and mammals have a four-chambered heart. 

The ventricle is divided by a septum into two compartments completely separating oxygenated from deoxygenated blood and delivering the maximum amount of oxygen to the head and body at the most efficient pressure. 
The four-chambered heart solves the dilution problem.


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