Blue Whale :- One of the largest animal known to have ever existed. The heart of an average sized blue whale weighs 400 pounds (180 kg) and is the largest known in any animal. During the first seven months of its life, a blue whale calf drinks approximately 380 litres (100 US gal) of milk every day. Blue whale calves gain weight quickly, as much as 90 kilograms (200 lb) every 24 hours