It’s almost Valentine’s Day, which means cartoon hearts are popping up on every card and candy box. But it’s the real, hardworking organs that deserve some love this holiday weekend.
An adult human resting heart rate is normally 60 to 100 beats per minute, while shrews clock in at “over 1,000 beats per minute—that’s over 16 times a second,” Mark Oyama, cardiology professor at the University of Pennsylvania School of Veterinary Medicine, says via email.
The pygmy shrew, which weighs in at less than an ounce, has the fastest heartbeat of any mammal at 1,200 beats per minute, according to the National Wildlife Federation. (See “Small Wonder: What Are the World’s Tiniest Animals?”)
Animal heart rates tend to correlate to their size, with smaller animals having quicker rates, Oyama explains.
Several whale species have heart rates as slow as 10 to 30 beats a minute.
The 100-foot (30-meter) long blue whale, the biggest animal on Earth, not surprisingly has the largest heart of any animal, weighing in at 400 pounds (180 kilograms).
Well, that’s physically. Many people would say the biggest heart in the world belongs to their dog.
Dogs do indeed have “slightly higher heart-to-body weight ratios than cats and other animals,” Oyama says. (Read “Healing the Heart” in National Geographic magazine.)
The average weight of a dog heart is about 0.7 to 0.8 percent of their body weight, whereas in cats it's about 0.35 percent.
Giraffe hearts aren’t unusually large for their size, Rachel Brand, an independent behavioral ecologist in Namibia, says via email—but you could say they’re a little one-sided.
A giraffe heart’s left wall ventricle can be up to 3.24 inches (about 8 centimeters) thick, compared with its right ventricle wall, which is about 0.6 inch (1.5 centimeters) thick. Thickness indicates muscle power.
That disparity is because the right side only has to pump blood to the lungs, while the left side has the tough job of pumping blood over 6 feet (about 2 meters) high to reach the giraffe’s head. (Related: “How Did Long-Necked Dinosaurs Drink Without Getting Dizzy?”)
Have a Heart … Or Three
When they were handing out hearts, some animals forgot to say when.
Cephalopods like squid and octopus usually have three hearts: One systemic heart that pumps blood through the rest of the body after the hearts have pumped it to the gills, where oxygen is taken up.
And then some animals have no heart at all.
Sea stars, aka starfish, and other echinoderms “do not have a ‘heart’ or anything analogous to it,” Chris Mah, a marine invertebrate zoologist at the Smithsonian National Museum of Natural History in Washington, D.C., says via email.
Nor do they have blood to pump with one.
Instead, starfish have millions of tiny, hairlike structures called cilia that beat constantly, pumping seawater via “a system of internal pipes and bags,” Mah says.
Their internal cavity also has “all the various cells needed for transporting nutrients, immune cells, and so forth.” (“Meet the Chocolate Chip Starfish and Its Unusual Relatives.”)
It’s okay if they’re heartless. We heart them anyway.