There are many types of whales in the world.
But some whales have special circulation system:they have 4 hearts
It's because to ensure that the brain and heart muscle have the best oxygen supply to conserve oxygen during a long dive. And another reason is because
the it has enormous body and hearts needs to be very strong that it can supply oxygen to the whole body.
P.S: Their hearts can be upto the size of a minivan to the size of a double decker bus.