Blue whales are the largest animals on Earth! Due to their size, their organs are very big! A blue whale’s heart is so big that a 6-year-old human could stand up inside of it!! Blue whales need such a big heart because they swim a lot and they need a stronger and bigger heart. Due to their size, the blue whales need big hearts in order to pump blood around their bodies. That is why blue whale hearts can be 5 feet tall!