For the first time ever, scientists have recorded the heart rate of the world’s largest creature: the blue whale. To get this reading, they attached an electrocardiogram device to the body of a whale. They found that the mammal’s heart rate can slow to just two beats a minute as the animal searches for food below the surface of the ocean. The highest heart rate they recorded was 37 beats a minute after the whale returned to the surface for air. The team’s study appears online in the publication Proceedings of the National Academy of Sciences. The blue whale is the largest animal that has ever lived. It can grow to 30 meters long and weigh as much as 181,000 kilograms. The animal’s heart alone weighs more than a fully grown cow.