How much does a blue whale's heart weigh?

A blue whale’s heart weighs about 400 pounds, roughly the weight of a large piano.

Blue whales are the largest animals known to have lived, reaching around 100 feet or more in length and weighing well over 100 tons. Their enormous bodies require a powerful circulatory system to move blood through a huge network of vessels, helping deliver oxygen to muscles and organs.

The heart is correspondingly immense. Its exact weight can vary with the individual and the measurement method, so 400 pounds is an approximate figure rather than a precise value for every blue whale. The often-repeated comparison to a studio piano is meant to give the measurement a relatable scale.

A blue whale’s heart is also notable for its very slow resting heartbeat, which can fall to only a few beats per minute during deep dives. When the whale surfaces, its heart rate rises as it replenishes oxygen.