(N/A) In birds and mammals,the heart is four-chambered with a complete partition of the ventricles.
This structural adaptation ensures that deoxygenated blood is received by the right atrium and right ventricle,while oxygenated blood is received by the left atrium and left ventricle.
Because the ventricles are completely separated,there is no mixing of oxygenated and deoxygenated blood within the heart.
This separation allows for the formation of two independent circulatory pathways: the systemic circulation and the pulmonary circulation.
This efficient double circulation ensures that highly oxygenated blood is delivered to the tissues,which is essential for meeting the high energy demands required for maintaining a constant body temperature (endothermy) in these organisms.