Not including lawyers and politicians, the mammal with the smallest heart in the world is the Etruscan Pygmy Shrew, with the bumblebee bat of Thailand coming in a close second.
The Etruscan Pygmy Shrew is also known as Savi’s pygmy shrew and White-toothed Pygmy Shrew.
Both are about the size of a bumblebee or an adult thumbnail, and weigh up to 3 grams. The shrew is usually a little smaller than the bat, which appears much larger than it is when it spreads its wings.
Although they have tiny bodies and body parts, these mammals have a much larger heart relative to their body size than any other mammal.
Even with larger hearts they have really high heart rates to help pump blood around their bodies. The Etruscan Pygmy Shrew’s heart beats at an amazing 1,200 beats per minute. These animals have very high metabolic rates, and they have to eat constantly to avoid starvation.
On the other side of the scale, the blue whale’s heart rate is somewhere between 10 and 30 beats per minute, and a healthy human’s resting heart rate is about 60 to 80 beats per minute.
It seems that smaller mammals have much higher heart rates than bigger ones.