Is a blue whale’s heart as big as a car?

Not in weight. The only blue whale heart ever recovered and preserved weighed about 175 to 180 kg (roughly 390 to 400 lb), about as much as two or three adult people. In size, though, a dilated heart is big enough that the technician who preserved it said it could just be squeezed into a Smart car.

The “size of a car” line is one of the most repeated facts about the largest animal that has ever lived, and it is half right. A blue whale heart is enormous by any normal standard. With its great vessels attached it stands about two metres (six and a half feet) tall, and it is the largest heart known from any animal. But it weighs a small fraction of what a car weighs, and it would not fill an ordinary family car’s cabin. The comparison works only for the very smallest cars and only for volume, not mass. This page explains where the real numbers come from, how the heart was measured and preserved, how fast it beats, and what it tells scientists about the limits on how big an animal can grow. For the animal itself, see blue whale.

Where did the real blue whale heart come from?

From a female blue whale that died in sea ice off Newfoundland in 2014 and washed ashore at Trout River, where a team from the Royal Ontario Museum cut it out.

In March 2014, nine blue whales were found dead near the Cabot Strait, between Newfoundland and Cape Breton Island, after becoming trapped in heavy sea ice. The loss was significant: the Smithsonian reported that it reduced the Northwest Atlantic blue whale population by about 3%. Two of the carcasses drifted ashore on the west coast of Newfoundland that spring, one of them at the small town of Trout River. For scientists it was a rare opportunity. Blue whales almost never strand in a condition that allows dissection, and no blue whale heart had ever been recovered and preserved.

The Royal Ontario Museum (ROM) in Toronto sent a team led by mammalogy technician Jacqueline Miller, working with Research Casting International and veterinarians from Lincoln Memorial University. The paper describing the work, published in the Journal of Plastination in 2017, records the specimen as a mature female 23 m (76 ft) long; the same paper gives 32 m in a later section, a discrepancy that the 23 m figure in the methods most likely resolves, since 32 m would exceed the longest blue whale ever reliably measured. The second carcass was another female of about 24.5 m.

Getting the heart out was heavy physical work. The team cut a window through the ribs, and Miller and four colleagues pushed the heart out of the chest cavity into a large dumpster bag. The heart was then frozen. The plastination paper gives its weight as 175 kg (386 lb); the Smithsonian, describing the same organ, put it at nearly 400 lb; and other reports have rounded it to 180 kg or even 200 kg (440 lb). These figures are close enough to agree on the essential point: well under a quarter of a tonne.

How was the heart preserved?

By plastination, the process used for human anatomy exhibitions, in which the water and fat in tissue are replaced with silicone polymer. It took about three years from recovery to display.

The heart was stored frozen at −20°C for more than a year before it was thawed in June 2015. The team flushed it, dilated it to restore its natural shape and fixed it in formaldehyde; the Smithsonian put the volume of formaldehyde solution at 2,800 litres. It was then shipped in a refrigerated truck to Gubener Plastinate GmbH in Guben, Germany, the company founded by Gunther von Hagens, the inventor of plastination, arriving on 27 November 2015.

The process at Guben was slow and chemical-heavy. Dehydration in cold acetone took 42 days with five acetone changes, and a second stage to remove fat took about four months; in all about 22,000 litres of acetone were used. Impregnation with silicone polymer, under a vacuum that was lowered gradually from 150 millibar to 5 millibar, began on 4 August 2016 and ran until mid-December 2016. Red and blue polymer was injected to show the arteries and veins, a window was cut into the right ventricle so visitors could see inside, and the heart was supported on an internal frame. The finished specimen measures about 96 cm wide and 106 cm long, not counting the great vessels.

The heart flew back to Canada and went on display at the ROM in 2017 in the exhibition “Out of the Depths: The Blue Whale Story”, alongside the skeleton of another blue whale recovered off Newfoundland. Miller’s comment about the Smart car came from that period: once dilated, she said, the heart was large enough to squeeze into one. That is the origin of the most defensible version of the car comparison.

Why do people say it is the size of a car?

Partly because of genuine size, partly because estimates made before anyone had weighed a real heart were much higher, and partly because the claim makes a good story.

Before 2014, nobody had weighed and measured a whole blue whale heart under modern conditions, so books and documentaries relied on estimates. One way to estimate heart size is by scaling from other mammals. Standard mammalian scaling equations predict that heart mass rises roughly in step with body mass. Using those equations, the scientists who measured a wild blue whale’s heart rate in 2019 calculated that a 70-tonne whale would be expected to have a heart of about 319 kg, pumping about 80 litres of blood per beat. Scale the same reasoning up to the largest blue whales, which have been recorded at 173 tonnes with estimates up to 199 tonnes, and simple proportion gives hearts of roughly 700 to 900 kg. Large estimates of that kind, applied to the biggest whales, probably helped feed the “car-sized” image.

The heart actually recovered came from a 23 m female, an average-sized adult rather than a record animal, and it weighed about 175 kg. That is noticeably less than the scaling prediction, though without knowing her exact body mass the comparison is rough. It is possible that the hearts of the very largest blue whales, especially those of the Antarctic whaling era, were considerably heavier. But no such heart was ever weighed and kept, so the one measured heart is the honest benchmark. Even on generous assumptions, a blue whale heart is roughly the weight of a large motorcycle or a golf cart, not a car, which typically weighs well over a tonne.

A second myth often travels with the first: that a person could swim through the whale’s arteries. The great vessels are large, but not wide enough for an adult to swim through. The point of these comparisons is to make an extraordinary animal imaginable, and the real numbers are extraordinary enough without inflation.

How fast does a blue whale’s heart beat?

As slowly as 2 beats per minute at the bottom of a dive and as fast as about 37 beats per minute just after surfacing, according to the only heart-rate record ever taken from a wild blue whale.

The data come from a 2019 study in the Proceedings of the National Academy of Sciences led by Jeremy Goldbogen of Stanford University, with colleagues including John Calambokidis. The team attached a suction-cup tag carrying an electrocardiogram (ECG) and depth recorder to a single free-diving blue whale in Monterey Bay, California, without capturing or restraining the animal. Photo-identification records showed the whale was a male at least 15 years old, first sighted in 2003 and previously seen off Southern California and in the Gulf of California. The tag recorded 8.5 hours of heart rate and depth.

The whale made foraging dives as long as 16.5 minutes and as deep as 184 m, with surface intervals of one to four minutes between them. During dives his heart rate was typically 4 to 8 beats per minute, and at its lowest just 2. At the surface after a deep dive it rose to 25 to 37 beats per minute. By comparison, standard equations predict a resting heart rate of about 15 beats per minute for a 70-tonne mammal, so during the bottom phase of a dive the whale’s heart was beating at one-third to one-half of its predicted resting rate. At the other end, the researchers calculated from the ECG that each beat at the surface took about 1.8 seconds, which sets an approximate upper limit of 33 beats per minute. The observed surface rates of up to 37 were therefore at or near the maximum the heart could physically achieve.

Feeding produced a striking pattern. Blue whales feed by lunging at swarms of krill, accelerating and engulfing a volume of prey-laden water larger than their own body. During the powered upward phase of each lunge, the whale’s heart rate rose to about 2.5 times its minimum, then fell gradually during the long glide as the engulfed water was filtered out through the baleen. Lunges are estimated to raise the whale’s metabolic rate to about 50 times its resting level, which helps explain why heart rate climbs during this phase even in the middle of a dive.

Why does the heart beat so slowly?

To save oxygen. Slowing the heart is the core of the mammalian dive response, and the blue whale shows it at an extreme.

All diving mammals slow their hearts when they submerge, a response called bradycardia, and constrict blood vessels to the skin, gut and many muscles so that oxygen-rich blood goes mainly to the brain and heart. A slower heartbeat also means the heart muscle itself uses less oxygen. In a blue whale the problem is especially sharp because its muscles store relatively little oxygen: the PNAS study notes that blue whale muscle contains about 0.8 g of myoglobin per 100 g, five to ten times less than in most marine mammals. That places more of the burden on oxygen carried in the blood, and on how carefully the heart rations it.

A beat every 30 seconds raises an obvious question: how does blood keep flowing in between? The answer lies in the aorta. Rorqual whales, the family that includes blue, fin and humpback whales, have a large-diameter, highly elastic aortic arch. Each beat stretches it, and as it recoils it keeps pushing blood onwards through the long pause until the next beat, smoothing out what would otherwise be violent pulses. At the surface, when the heart rate rises above about 20 beats per minute, the authors suggest that the size and stiffness of the aorta cause reflected and outgoing pressure waves to interfere and partly cancel, which lowers the resistance the heart must work against while it races to reload oxygen. For how whales store oxygen in their lungs, blood and muscles, see how much lung capacity marine mammals use.

Does the heart limit how big a whale can grow?

Possibly. The 2019 study found the blue whale heart working close to its physical limits at both ends of its range, which suggests cardiovascular constraints may help cap maximum body size.

The researchers framed their study as a test of physiological limits at the largest scale. On a dive the heart already beats far below its predicted resting rate; at the surface it runs near its estimated maximum to recharge the blood with oxygen in a few minutes. There is little room left in either direction. Feeding adds another squeeze: because the volume of water a rorqual engulfs increases faster than body size, larger whales must do relatively more work in less time on each dive. Together, the authors argue, these demands mean blue whales likely face several physiological constraints during both the dive and the surface interval that may have limited the evolution of even bigger bodies. A heart rate study of one whale cannot settle the question, but it is the first direct evidence from the biggest heart on Earth.

For the species, the more pressing limit is human. The blue whale is listed as Endangered by the IUCN. Estimates compiled for the 2018 assessment put the world population at roughly 5,000 to 15,000 mature individuals, or 10,000 to 25,000 in total, a fraction of the numbers before 20th-century commercial whaling. The North Atlantic population that produced the Trout River heart is thought to number only about 1,000 to 3,000. The nine whales lost in the ice in 2014 were a reminder of how much a single bad event can matter at those numbers. For the latest estimates, see how many blue whales are left.