In this review, causes of tremendous differences in respiration and oxidative metabolism between the homoiothermal and poikilothermal vertebrates are discussed. Tissues of the latter contain not lower, and sometimes even higher amount of mitochondria with the powerful potential of oxidative enzymes, as compared with the homoiothermal vertebrates; this potential is realized only by 3-4% because of a low rate of oxygen transport due to peculiarities of the cardiovascular system of the lower vertebrates. Limitation of ATP synthesis is responsible for a specific structure of plasma membranes with the essentially lower amount of channels for the passive ion leakage as compared with the mammalian plasma membranes. Examples are presented of the homoiothermal animal cells (the frog olfactory receptor cell) that contact with environment without mediation of the blood circulation system and have the energy metabolism level comparable with that of mammalian cells. Examples of energetic aromorphosis are tunas with heat exchangers in several organs and with a powerful system of oxygen delivery to cells; owing to this, intensity of their oxidative metabolism could reach that of the higher terrestrial vertebrates. The closing part of this paper describes the molecular mechanisms that allow some representatives of reptiles, amphibians, and fish to survive long periods of hypoxia and anoxia.