The largest heart in the animal kingdom belongs to the blue whale

At the start of this year, we talked about the blue whale (Balaenoptera musculus). Today we wanted to dive deeper into a specific part of their giant anatomy: their heart! It’s no surprise that blue whales have huge hearts since they are one of the largest animals ever to exist. Not only are these organs huge and efficient, but they also serve an important ecological purpose even after death. A blue whale heart can be 5ft tall (1.5m), weigh over 400 pounds (200kg), and have tubes as large as the tubes in a jungle gym for small children!

How does this big heart work?

Blues whales are one of many species that seasonally migrate to reach their feeding or breeding habitats. They can travel thousands of miles. During their travels, they may also need to dive for protection. These gentle giants need large, powerful muscles and organs to accomplish these feats.

Compared to the average human heart rate of 60-100 beats per minute, the heart rate of a blue whale can range from 2-10 bpm when submerged to 25 – 37 bpm at the surface. The heart rate of a blue whale is also surprisingly “elastic”; it is notably slower during deep dives. A lower heart rate helps the whale to preserve the oxygen levels in their blood and keep their vital organs functioning.

The blue whale’s large muscular heart keeps the blood flowing when the pressure increases in the deep waters. It takes an extremely powerful muscle to pump 10 tonnes of blood through a huge body at such great depths. A slowly contracting aorta (the artery that moves blood to the rest of the body) is what researchers believe is responsible for the blue whale’s heart rate efficiency. Unlike a straightforward open-and-close valve (like us humans), having elastic contractions could allow the blood to flow in between heartbeats. It is an incredibly efficient way to save energy while diving.

With time, more research will be done on the blue whale’s physiology, but what we know so far is pretty fascinating!

A mother’s big heart

Though not necessarily connected to its anatomical size, there is evidence that blue whales, like other rorquals, have maternal bonds with their calves through the first year or so of their lives. Female blue whales give birth every 2-3 years, which means that the population grows slowly. Because of this, calves must be well protected until they can fend for themselves. Mothers need time to teach their children the skills they will need to survive in the future, such as avoiding predators.

A nutrient-rich heart is targeted by hungry predators

Unfortunately, the large size of the whales cannot protect them from every threat. In a recent study, killer whales have been confirmed to actively hunt and kill an adult blue whale. A dozen killer whales participated in one of the observed hunts, and around 50 individuals enjoyed the feast for about 6-hours after the blue whale’s death. Killer whales attacked the giant’s head during the feast to consume the tongue. There is no photo evidence of killer whales feeding directly on the heart, but one can assume they do, considering the heart is incredibly nutrient-dense.

What happens to the heart after the whale’s death?

After their death, whales often fall to the depths where their bodies become a source of food and shelter for the light-starved creatures of the deep. Known as a whale fall, the protein-rich heart, along with the other organs of this giant whale, sustain life and add much-needed nutrients to the surrounding ecosystem. It is another example of how different parts of the marine environment are connected. Hence, the survival of blue whales and any impact that threatens their ecosystem balance could have significant consequences for the whole marine world.

Sources & further reading

• Goldbogen, J. A., et al. “Extreme bradycardia and tachycardia in the world’s largest animal.” Proceedings of the National Academy 
• Totterdell, John A., et al. “The first three records of killer whales (Orcinus orca) killing and eating blue whales (Balaenoptera musculus).” Marine Mammal Science.
• The Speak Up For Blue podcast. A generally great listen about ocean science and conservation news.

Interested in reading about another rorqual? Check out this post on the Sei Whale!

The Sei Whale – November 2020