A blue whale's heartbeat has been recorded for the first time - and the results are fascinating

For the first time, scientists have recorded the heart rate of a blue whale, uncovering new information about the biology of the world's largest mammal.

After measuring the heart rates of diving emperor penguins and captive whales, researchers from the University of Stanford decided to try to measure the heart rates of wild whales.

Using suction cups, biologists attached electronic sensors to a blue whale's left flipper to measure its heart rate -- with surprising findings.

The experts discovered that the blue whale lowered its heart rate to as little as two beats per minute when it dived for food.

At the bottom of a foraging dive, the whale's heart rate increased to about 2.5 times the minimum, then decreased again. Once the mammal began to surface, its heart rate increased again.

The animal's highest heart rate -- between 25 and 37 beats per minute -- occurred at the surface when it was breathing and restoring oxygen levels, scientists said in research published in Proceedings of the National Academy of Sciences Monday.

Blue whales, which can reach up to about 30 meters in length, are thought to be the largest mammals to have ever lived.

According to the scientists, analysis of the data suggests that the blue whale's heart is "working at its limit," and may provide clues as to why blue whales have not evolved to be bigger.

"Animals that are operating at physiological extremes can help us understand biological limits to size," Jeremy Goldbogen, assistant professor of biology in the School of Humanities Sciences at Stanford and lead author of the paper, said in a statement.

"They may also be particularly susceptible to changes in their environment that could affect their food supply.

"Therefore, these studies may have important implications for the conservation and management of endangered species like blue whales," he added.

Researchers added that the findings were interesting because the whale's highest heart rate almost outpaced predictions, while the lowest heart rate was about 30% to 50% lower than expected.

Scientists are hoping to try the tag on other whales, such as humpbacks, minke whales and fin whales.