For the first time, researchers have measured the heart rate of the world’s largest mammal, a blue whale, in the wild—and the results are extreme. The team attached heart rate monitors to one whale with suction cups so they would stay secure as the animal lunged open-mouthed through the water collecting krill. After recording for nearly 9 hours, the team found that the whale’s heart rate plummeted to as low as two beats per minute as it dived deep, then rocketed back up when the whale resurfaced, peaking at 37 beats per minute, New Scientist reports. The whale’s slow heart rate while diving is especially surprising given the amount of energy the whales expend catching their food, the researchers say. The low rate probably allows the whales to temporarily redistribute oxygen to muscles throughout their body as they lunge through the water, they report this week in the Proceedings of the National Academy of Sciences.