A blue whale's heart is roughly the size of a small car.

The longer version

Size in mammals scales with body mass, and the largest animal alive pushes that relationship to its limit. An organ that pumps blood through a body tens of metres long must be enormous, thick walled and slow beating, because moving that volume of fluid takes real force.

The heartbeat of a blue whale is remarkably slow when the animal dives, dropping to just a few beats per minute, while at the surface it rises to support active swimming. Thick arterial walls and elastic vessels smooth out each contraction so the pulse does not damage delicate tissue. Recordings of the sound show a low thud far below what the human ear handles well.

Where this entry sits

This collection gathers small surprises about mammals, reptiles, amphibians, birds, fish, insects, and the pets living alongside people. Expect odd details about senses, anatomy, and everyday behaviour that many people never notice in the animals around them. The full list sits on the Animals page, where every entry is listed in order.