How Big Is a Blue Whale's Heart? Facts vs Popular Myths

How big is a blue whale’s heart?

Like all mammals, the blue whale has a heart with four chambers: two atria that receive blood and two thick-walled ventricles that pump it out. Only the scale is different. The heart preserved by the Royal Ontario Museum (ROM) in Toronto weighed about 175–180 kg (385–400 lb) before preservation, and some reports give figures of up to about 200 kg (440 lb). Measured from the top of the aorta to the bottom of the lowest chamber, it stood about 1.5 m (5 ft) tall.

After preservation, the heart itself measured about 106 cm (42 in) long and 96 cm (38 in) wide. It is roughly as big as a large armchair.

In proportion to its body, the heart is not oversized: about 180 kg is only a fraction of 1% of the weight of a whale that may weigh around 100 tonnes. See How big is a blue whale? for the size of the rest of the animal.

Where did the Royal Ontario Museum heart come from?

In early 2014, at least nine blue whales died after being trapped in heavy sea ice off the southwestern coast of Newfoundland, Canada. They belonged to the small, endangered population of the northwestern Atlantic. That spring, two of the carcasses drifted ashore near the towns of Trout River and Rocky Harbour.

A ROM team traveled to Newfoundland in May 2014 to salvage the skeletons. They also removed the heart of the Rocky Harbour whale, a mature female about 23–24 m (76–79 ft) long, and froze it. It was the first time a blue whale heart had been recovered for permanent preservation.

In late 2015 the heart was shipped to a specialist laboratory in Guben, Germany, to be plastinated. In this process the water and fat in the tissue are slowly replaced with silicone, leaving a dry, durable specimen. The work took more than a year and used about 22,000 liters of acetone and some 5,000 liters of silicone mixture. The finished heart went on display in Toronto in 2017 in the exhibition Out of the Depths: The Blue Whale Story.

How fast does a blue whale’s heart beat?

For a long time, nobody knew. In 2018, a team led by Jeremy Goldbogen of Stanford University attached a sensor tag with suction cups to a wild blue whale in Monterey Bay, California. Electrodes inside the cups picked up the electrical signals of the heart, the same kind of trace a hospital ECG records. The results were published in 2019.

During feeding dives, the whale’s heart rate fell to an average of about 4–8 beats a minute and sometimes to just 2. At the bottom of a dive, as the whale lunged at krill, the rate rose to about two and a half times its minimum. Back at the surface, while the whale breathed and reloaded its body with oxygen, the heart raced at 25–37 beats a minute.

Why does the heart slow down during dives?

Slowing the heart is part of the dive response shared by whales, seals and other diving mammals. With fewer beats, blood is sent mainly to the organs that need it most, such as the brain and heart, and stored oxygen lasts longer. Learn more about breath-holding in How do whales breathe?

The researchers suggested that a stretchy, elastic aortic arch helps the whale manage such slow beats. After each beat, the wall of this large artery slowly springs back, which keeps blood flowing to the body between beats. For the depth records of other whales, see How deep can whales dive?

Myth: a blue whale’s heart is the size of a car

This is the most famous blue whale “fact”, and it is exaggerated. The claim is often given as the size of a Volkswagen Beetle. A classic Beetle is about 4 m (13 ft) long and weighs roughly 800 kg (1,760 lb), several times as heavy as the measured heart. The ROM heart is a very large organ, but it would fit easily inside a car with room to spare.

Myth: a child could swim through its arteries

Another common claim is that a small child could swim, or an adult could crawl, through a blue whale’s blood vessels. The aorta, by far the widest artery, is often described as roughly as wide as a dinner plate. That is enormous for a blood vessel, but nowhere near wide enough for a person to move through, and the arteries that branch off it quickly become much narrower.

Myth: its heartbeat can be heard miles away

You may read that a blue whale’s heartbeat can be heard 3 km (2 miles) away. There is no scientific recording showing this. The whale’s loud, low calls can travel hundreds of kilometers underwater, but heartbeats are far quieter. In the 2019 study, scientists had to place electrodes directly against the whale’s skin to detect them.

Does the heart limit how big whales can get?

The lowest heart rates recorded in 2019 were about 30–50% below what scientists had predicted for an animal of this size, and the highest came close to the predicted maximum. The team suggested that the blue whale’s heart may already be working close to its physical limits. A bigger whale would need even more energy, and its heart might not keep up.

If this idea is correct, it could help explain why no animal has grown larger than the blue whale. It remains a hypothesis rather than a proven fact, based on measurements from a single whale.