An octopus, like its other comrades in the cephalopod world, has three hearts. Two hearts are dedicated to pumping blood to the gills, while the other takes care of the rest of the body. Unlike humans, octopuses have blue blood. Their blood lacks hemoglobin, the protein that gives human blood its red color. Instead, they rely on the copper-rich protein hemocyanin to perform oxygen transport duties, as it is more efficient in low-temperature and low-oxygen environments.[2]Ever wondered why octopuses spend more time crawling than swimming? The answer: fatigue. Because the heart powering the body stops beating when the octopus is swimming, it tires more quickly.
Pumping blood up to a giraffe’s brain takes a lot of power, and a human heart would not be up to the task. Luckily, the giraffe has the hardware to push blood all the way around its supersized body. At 60 centimeters (24 in) long and weighing in at 11 kilograms (24 lb), the giraffe heart is in the heavyweight division. Not only does blood need to defy gravity for 1.8 meters (6 ft) to get to the creature’s head, but it travels about the same distance to reach the giraffe’s feet. Gravity helps it on the way down, true, but once the blood gets to the bottom, there needs to be enough pressure behind it to get back up again. Otherwise, giraffes would have really fat ankles.Have you ever felt light-headed after standing up to quickly? That is the result of a sudden drop in blood pressure. Giraffes move their heads around a lot. They should be permanently dizzy. A combination of nifty adaptations prevents this, though. Giraffes have an unusual jugular vein. This is the vein that carries blood back to the heart from the head, and in most animals, it does not contain muscle. The giraffe’s jugular vein does. This muscled jugular vein, along with its thick skin and powerful ticker, increases the animal’s blood pressure to about twice that of humans.
It’s no surprise that the biggest animal on Earth has the biggest heart. But is the blue whale heart really the size of a small car? In the absence of actual blue whale specimens, scientists could only guess at the size of the giant mammal’s heart. In 2014, though, scientists from the Royal Ontario Museum embarked on an audacious mission: to preserve the remains of a blue whale that had perished in ice off Newfoundland. Most blue whale carcasses sink to the ocean floor, so this event provided a unique opportunity.Recovering the heart was a priority. Scientists opened the chest cavity before venturing inside the carcass to retrieve the heart. Waist-deep in blood and lungs, the scientists freed the heart from the surrounding tissue. It then took four of them to push it out through the opening they had made.The heart weighed 180 kilograms (400 lb) and was capable of pumping 150 liters (40 gal) of blood per beat. At 1.2 meters (4 ft) in diameter, it was not quite as big as a car but rather about the size of a golf cart. Still, retrieving a blue whale heart is not for the fainthearted.
Ah, cockroaches. The hearts of these much-maligned insects have 12 or 13 chambers, but rather than blood, the cockroach heart moves a whiteish/yellowish substance called hemolymph through their bodies. The nutrient-rich hemolymph nourishes the organs but does not carry oxygen, as insects are oxygenated through openings in their body surface. Even with the most powerful stethoscope, you will not detect a cockroach heartbeat. Their hearts do not beat. Muscles in the body cavity contract and relax to move the gooey hemolymph through the heart.
The prize for the mammal with the fastest heart rate goes to the pygmy shrew. Generally, the smaller an animal is, the faster its heart rate is—and the pygmy shrew is tiny. Sorex hoyi weighs about 3 grams, and you could lose one in your cereal bowl. The pygmy Shrew’s heart rate is over 1,000 beats per minute—or 16 beats per second! Pity the shrew embarking on a fitness regime. Imagine trying to monitor its target heart rate. It certainly wouldn’t be 220 minus age . . .