Sharks are "cold-blooded" (poikilothermic) animals, meaning their body temperature is the same as that of the water in which they live. The term cold-blooded is misleading, however, because sharks living in warm water are "warm-blooded" in actual temperature.
Some fast-swimming sharks in the Mackerel shark order (for example the mako and white sharks) can actually raise their core body temperature somewhat above that of their surroundings. In these sharks, heat generated as they swim is conserved by a special vascular network surrounding the muscles. This network helps to conserve heat in the body core, rather than allowing it to dissipate into the cooler water. Just as chemical reactions in a laboratory proceed faster when heat is applied, so too do metabolic reactions at higher temperatures. With their higher core body temperature, these species are able to be more active and efficient predators than most other sharks and bony fish.