Which animal has the fastest metabolism?

Very small warm-blooded animals lose heat rapidly, so they must burn energy at a furious rate to stay alive. The Etruscan shrew, one of the smallest mammals on Earth at around 2 grams, has a heart that can beat about 1,500 times a minute and must eat close to its own body weight in food each day. Hummingbirds have similarly extreme metabolisms, with hearts beating over 1,000 times a minute in flight and a need to feed almost constantly. These animals live life in the fast lane, always on the edge of starvation. Even a short time without food can be fatal for them.