Two separate circulatory pathways are present and there is no mixing of oxygenated and deoxygenated blood in the ventricles in

Whale is a mammal. In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation.