Heart: similar size to an eraser on a pencil tip. Has the largest heart of any animal relative to its tiny body mass.
Heart: just over a centimetre in size, but balloons to almost double this after a mighty feast, to help speed up digestion.
Heart: the largest heart of all land mammals, about 60 centimetres long. Heart beats around 170 times per minute to pump blood up its long neck.
Heart: weighs between 20 – 30 kilos, but only beats around 30 times a minute, making the elephant the largest animal with the lowest heart rate.
Heart: technically, the earthworm has no heart, but its five aortic arches help pump blood around the body.
Heart: around the size of two clenched fists, or nine centimetres wide, with male hearts weighing slightly more than female hearts.
Heart: it makes up a tiny part of its body weight, but rabbit hearts can beat up to 300 times per minute, meaning they can easily die of shock.
Heart: a similar size to a cricket ball, polar bear hearts are about 20 centimetres wide. Their heartbeat slows from 40 to 27 beats per minute when hibernating.
Heart: practically the same size as a human’s, pig hearts have been successfully transplanted into apes and pig valves are used in human transplants.
Heart: around three times the size of a human’s and about the size of a melon, a running horse’s heart can clock 240 beats per minute.
Heart: the heart size of a dog differs greatly by breed and gender, but in general terms, smaller dogs tend to have zippier heart rates than larger dogs.
Heart: around the size of a small car, whale hearts need to pump about 7,000 litres of blood, compared to five and a half litres in a human.