Among other things, the data reveals answers about the size of blue whales, the largest organisms to have ever lived on Earth.

Studying the details of blue whales isn’t the easiest thing to do. They are big, and they don’t live in tanks. And in big, reaching lengths of 108 feet (almost 33 meters). They are the largest animal to have ever lived on the planet, even surpassing the largest of dinosaurs. For more information, read these 7 facts about blue whales!

Because of this, recording the heart rate of one of these colossal cetaceans has been an elusive task. It’s not like you can just grab their wrist and take a pulse.

Stanford university went and figured out how to do it. They created a sensor-packed tag that could be applied by four little suction cups to an area near a whale’s fin.

The team managed to secure the tag on the first try and, over time, it slipped into position near the flipper where it could pick up the heart’s signals. This marks the first time that a blue whale’s heart rate had been recorded, and it revealed some surprises.

Stanford explains:

When the whale dove, its heart rate slowed, reaching an average minimum of about four to eight beats per minute – with a low of two beats per minute. At the bottom of a foraging dive, where the whale lunged and consumed prey, the heart rate increased about 2.5 times the minimum, then slowly decreased again. Once the whale got its fill and began to surface, the heart rate increased. The highest heart rate – 25 to 37 beats per minutes – occurred at the surface, where the whale was breathing and restoring its oxygen levels.

Illustration depicting how the blue whale’s heart rate slowed and quickened as it dove, fed and surfaced. (Credit: Alex Boersma)/CC BY 4.0

The researchers were surprised by how both the low and high ends outpaced their predictions – the lowest heart rate was about 30 to 50 percent lower than they expected it to be. And really, two beats a minute is pretty wild.

They found that a blue whale’s heart works near its limit, which could explain why blue whales haven’t gotten bigger – the energy needs of a larger body would be more than what the heart could sustain. And it may also explain why no other animal has ever been larger than a blue whale.

It’s fascinating, and a good reminder that research like this can help inform conservation efforts.

“Heart rate can give you so much more information than just about the metabolic rate; its reaction to stressful events, its reaction to feeding,” says Stanford in the video below. “In order to have any kind of conservation implication or any kind of big management or even any kind of understanding of, like, ‘how do the largest organisms to ever to have lived actually function?’ We can answer some of those basic questions now.”