The largest heart in the world beats twice a minute

The blue whale is the largest animal ever known to have existed: bigger than any dinosaur. It can approach thirty metres in length, and moving a body like that takes a pump to match: its heart weighs around 180 kilos, as much as an upright piano, and is the largest in the animal kingdom.

For decades nobody knew the rhythm it beat to. Taking the pulse of such an animal, free and in the open sea, seemed impossible. Until 2019, when a team from Stanford University managed to attach a suction-cup sensor to a blue whale in Monterey Bay and listen, for the first time, to its heart at work.

What they heard was extreme in both directions. During deep feeding dives, the heart slowed to two beats per minute: a radical saving of oxygen. Back at the surface to breathe, it raced to more than thirty-five, close to its physical limit.

That is the part that most intrigues scientists: the blue whale's heart already seems to be working at the very edge of what its tissue allows. Perhaps that is why no larger animal has ever existed — not for lack of ocean, but because no heart could keep up.