My cadaver’s heart was about the size of two hands clasped together in prayer, filling most of the mid-chest cavity from the breastbone to the spine and down to the diaphragm, the muscular drape that separates the chest from the abdomen. (Every time you take a breath, the beating heart, resting on the diaphragm, translates slightly downward.) The heart had the shape of a truncated ellipsoid, like a squat volcano tipped on its side. Its muscle—the myocardium—was stiff. Cardiac muscle utilizes energy to relax, not contract, so at death my cadaver’s heart went into a state of rigor mortis. The atria, the upper collecting chambers, sat behind the ventricles, the muscular pumping chambers. The right ventricle sat most forward in the chest. It was crescent shaped, its muscle fibers running circumferentially around its exterior. Our professor told us that if ever, as doctors, we had to insert a needle into a patient’s chest to drain fluid, the right ventricle is the first chamber we would hit.
A few snips and we released the heart from its beige scaffolding. A lab mate placed it on the cadaver’s forearm. “This guy really wears his heart on his sleeve,” he said. Gripping the organ like a Rubik’s Cube, I poked my fingers into the thin-walled central veins. It was hard not to lapse into thinking that it was just a piece of meat, a rubberized toy. The left ventricle had thick walls, a sign of high blood pressure. The inside of the right ventricle was a dense morass of fibers. Maybe there were stories written in that mossy tangle, but I didn’t see any. By the time we’d cleaved all the chambers open—storing the heart between sessions in a circular aluminum pan, like the kind used for baking pies—it had the color and texture of cooked beef.
Until then, it had been a mystery exactly how our cadaver had died. His ribs were just a bundle of sticks—thin and worn—so some in our group assumed he’d succumbed to one of the diseases that waste and ravage the body, such as tuberculosis or cancer. But when we finally dissected his heart, the answer was revealed. The aorta, the main artery that carries blood from the heart to the body, was marbled with a massive amount of hard, cholesterol-laden plaque. When we sliced open the left coronary artery, grit pushed back against the scalpel. Inside the artery was a long dark brown clot where an atherosclerotic plaque had ruptured. Blood-clotting platelets had surged like minnows to the site of injury, clumping together to form a thrombosis that blocked the artery, causing a heart attack and tissue death.* This was the mechanism that probably killed my grandfather, too (and, I worried, would eventually claim another of the Jauhar men). Baked into those coarse arterial impurities, I couldn’t help but think, were my cadaver’s failures and sorrows.
With the chest open, we were reminded once again of the basic scheme that sustains all mammal life. Deoxygenated blood passes from the right atrium through a one-way valve, the tricuspid, into the right ventricle, which pumps the blood into the lungs. Oxygen-rich blood returns from the lungs to fill the left atrium. The blood then passes through another valve, the mitral (so named because it resembles a bishop’s miter, or headdress), into the left ventricle, from which it is pumped through the aorta and to the rest of the body. The blood eventually collects in two great veins, the inferior and superior venae cavae, which return it to the right atrium, where it again passes through the tricuspid valve into the right ventricle, to begin the cycle again.
This system, fundamental to all mammals, was not discovered until the early seventeenth century. For most of human history, the biological function of the heart was a mystery. Ten thousand years ago, Cro-Magnon hunters in Europe knew about the heart—they engraved curlicue pictures of it on the walls of caves—but they had no clue about what it did. Seven millennia later, the ancient Egyptians devised surprisingly prescient theories about the heart’s purpose. They believed the heart was where the soul resided, of course, but a classic document, the Ebers Papyrus, also described the heart as the center of the blood supply, with vessels directed toward the major organs. “The actions of the arms, the movement of the legs, the motion of every other member is done according to the orders of the heart that has conceived them,” the paper reads. Three thousand years later, the ancient Greeks had a mostly symbolic understanding of the heart. They believed the heart’s central location in the body meant that it was the center of life and morality. Plato also proposed that the heart was a sentry—the thymos, the highest part of the mortal soul—through which blood rushes to warn that something is amiss. In fact, this remains a more or less accurate description of the onset of the fight-or-flight response.
Circulation scheme in mammals (Created by Liam Eisenberg, Koyo Designs)
The Greeks relied on analogy—on metaphors—to try to understand the heart’s true purpose. But their fanciful speculation gave way when Galen, physician of the Roman emperor Marcus Aurelius and the towering figure in Western medicine from the third to the seventeenth century, applied a rudimentary scientific method rooted in observation and animal dissections—but still relying on symbols—to the problem of circulation. Drawing conclusions from surgeries on wounded gladiators, as well as vivisection on an array of animals, including cats, dogs, sheep, and lynx—human dissections were banned—Galen proposed a scheme in which the liver converts food into blood that, like water in an irrigation ditch, travels one way into the body to be absorbed and disappear, never to be used again. In Galen’s scheme, blood was sucked from the liver into the right ventricle and passed to the left ventricle through invisible pores in the wall—the septum—separating the two chambers. Once the blood entered the left ventricle, he believed “vital spirits” were added to it. The left ventricle then generated heat like a furnace to circulate the blood through fleshy pipes to the rest of the body. “In hardness, tension, general strength, and resistance to injury,” Galen wrote, “the fibers of the heart far surpass all others, for no other instrument performs such continuous, hard work.”
Galen’s theories were accepted as the final word on cardiovascular—indeed all human—anatomy in the West. Through the Middle Ages, his writings were scripture, immune to questioning. People focused on his conclusions, not the (often scant) observations upon which his conclusions were based. Though his reasoning was often spurious and analogical—water irrigating fields, a furnace heating pipes—the scientific method, careful measurement supporting or disproving falsifiable propositions, had not yet taken hold. When observations were made that did not concur with Galenism, they were marginalized and discounted.
A more advanced understanding of the heart probably existed in Persia, where the physician Ibn al-Nafis wrote his Commentary on Anatomy in 1242. Ibn al-Nafis was born in Syria and received his medical education in Damascus, before moving to Cairo. In Commentary, one of the pinnacles of the “golden age of Islamic medicine,” Ibn al-Nafis wrote that the ventricles receive nourishment from coronary vessels—not, as Galen had claimed, from blood deposited inside their chambers—and that the pulse is due to the force of cardiac contraction, not, as Galen contended, because of innate arterial contractility. Perhaps most important, Ibn al-Nafis asserted that there are no pores in the wall between the two ventricles. “There is no passage between these two cavities; for the substance of the heart is solid in this region and has neither a visible passage, as was thought by some persons, nor an invisible one which could have permitted the transmission of blood, as was alleged by Galen.”
However, despite these essentially correct insights, Ibn al-Nafis’s tome was unavailable in Europe and was mostly forgotten until a copy of it was discovered by a graduate student in the Prussian State Library in 1924. And so the workings of the heart remained a mystery in the West, “more deeply hidden than the step of the black ant on black rock in the black of night,” as al-Ghazali, the Islamic mystic, declared.
Fortunately, the prescientific vitalism that dominated European thought gave way to the Renaissance and a greater commitment to investigation and reason. Perhaps no thinker of this period did more to advance knowledge of the heart than Leonardo da Vinci, who considered it “an admirable instrument invented by the Supre
me Being.” Among hundreds of Leonardo’s anatomical illustrations, a great many are devoted to the cardiovascular system. His earliest studies were on pigs and oxen, but he also dissected human cadavers—about thirty in all, from infants to centenarians—that he collected from hospitals in Florence and Rome. Leonardo, like his predecessors, used natural phenomena and analogies to elucidate the workings of the heart. For example, he observed that water flowing against the banks of a river contributes to a river’s tortuous meanderings, and relying on this metaphor, he hypothesized that a similar thing happened with blood vessels. Leonardo constructed glass models of the aorta and the aortic valve to investigate the dynamics of blood flow using dyed water.* His dissections also provided insights into vascular disease. “The artery and the vein acquire so great a thickness of skin that it contracts the passage of the blood,” he wrote in a more or less accurate description of atherosclerotic plaque obstructing blood flow. However, the concept of a continuous, unceasing circulation eluded him.
Before a century had passed, raucous crowds were gathering at the University of Padua for public dissections. It was here—the center of European anatomy, where the world’s first anatomical theater housed galleries for spectators—that perhaps history’s greatest surgeon, Andreas Vesalius, worked. Vesalius’s portrait hung prominently in our anatomy lab in St. Louis, his watchful eyes scrutinizing our dissections like a high priest’s. The son of an apothecary, Vesalius was dissecting rats and dogs as a teen. As an academic, he performed his investigations on corpses stolen from graves and charnel houses outside Padua. He snuck them home inside his coat and stored them (unpreserved) for weeks in his apartment. A friendly criminal judge also gave Vesalius access to the gallows and even scheduled executions at times convenient to the anatomist. In De humani corporis fabrica (The Fabric of the Human Body), published in 1543 and perhaps the most venerated anatomy textbook ever written, Vesalius corrected many of Galen’s mistakes about the heart, especially his claim of a porous septum between the left and the right ventricles. Vesalius rightly deduced that to get to the left side of the heart, blood must pass through the lungs. However, he also reinforced some of Galen’s erroneous conclusions, such as that blood is produced by the liver and consumed in the body and that the heart is a furnace.
It wasn’t until William Harvey, the brilliant English anatomist who studied at Padua in his early twenties, that Galen’s theory of circulation was fully upended. Harvey was born in Kent in 1578 and completed his degree in arts at Cambridge when he was nineteen. He then transferred to the University of Padua to study medicine. Although Harvey discovered the mechanism of circulation in 1615, he waited thirteen years before publishing his results. He feared for his safety; challenging Galenic dogma was considered sacrilegious. He might have been worried that he’d suffer the same fate as Michael Servetus, a theologian who was burned at the stake in Geneva at the age of forty-two, in part for promoting the idea that blood passes through the lungs. “What remains to be said upon the quantity and source of the blood which thus passes,” Harvey wrote, “is of a character so novel and unheard-of that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies.”*
Portrait of William Harvey (From Domenico Ribatti, “William Harvey and the Discovery of the Circulation of the Blood,” Journal of Angiogenesis Research 1 [2009]: 3)
In De motu cordis, a seventy-two-page monograph written in Latin and published in 1628, when Harvey was fifty, Harvey set as his task “to look a little more deeply into the matter [of circulation]; to contemplate the movements of the arteries and of the heart not only in man, but also in other animals.” At first, he wrote, “I found the task so truly arduous … that I was almost tempted to think … that the movement of the heart was only to be comprehended by God.” Harvey decided to study the hearts of fish and frogs, whose contractions were slow enough to be analyzed. He also experimented on live and dead humans. In a simple but ingenious experiment, Harvey tied off a human arm with cloth, cutting off blood flow. He then relaxed the tourniquet so that arterial blood at higher pressure could pass but venous blood could not. The arm quickly swelled, leading Harvey to infer that blood flowed down arteries and drained through invisible connections into veins before returning to the heart. The nature of these connections—today we would call them capillaries—was a puzzle that Harvey never solved.† However, it did not deter him from his fundamental conclusions: that the heart is a pump, and that blood circulates continuously in a closed circuit from the arteries to the veins and back again.
Harvey’s opus is filled with references to Galen’s work, but as is so often the case in science, the student surpassed his teacher. When Harvey tied off a section of artery with two ligatures and cut it open, he discovered that there was only blood inside, not air or spirits, as Galen had claimed, or “sooty vapours,” as Harvey disdainfully called them. Of the tiny holes in the ventricular septum that Galen said allow blood to pass from the right ventricle to the left, Harvey wrote, “Damme, there are no pores. It is not possible to show such.”* He correctly deduced, as a few others had before him, that the flow had to be through the lungs. Harvey calculated that if the average adult heart expels two ounces of blood per beat (roughly true) at seventy-two beats per minute, the liver would have to produce five hundred pounds of blood from food per hour if blood were consumed as a nutrient, an obvious impossibility. Therefore, in Harvey’s scheme, blood was the transport vehicle for nourishment, not the nourishment itself. Like Galen and the natural philosophers before him, Harvey relied on metaphorical reasoning. “The heart is the center of life, the sun of the Microcosm, as the sun itself might be called the heart of the world,” he wrote. But Harvey’s metaphors—the circular motion of planets, the recycling of water on earth—were better suited for the problem of circulation.†
Though Harvey solved a problem that had vexed philosophers for millennia, perhaps his greatest contribution was in demonstrating the power of experiment to confirm or reject hypotheses. In his Harveian Oration in 1906, Sir William Osler, the Canadian physician, said of De motu cordis, “At last came the age of the hand—the thinking, devising, planning hand, the hand as an instrument of the mind, now reintroduced into the world in a modest little monograph from which we may date the beginning of experimental medicine.” However, despite his fundamental discoveries, Harvey never understood the purpose of circulation. He figured out the how of circulation but not the why. In his book he wrote that blood “returns to its source, the heart, the inner temple of the body, to recover its virtue.” But what was that “virtue”? And why was there a difference in color between crimson venous and cherry arterial blood? The answers to these two questions are of course the same. But Harvey and his followers were unaware of the oxygen-carrying function of red blood cells—indeed, ignorant of oxygen itself. Those discoveries would have to wait a hundred years.
Today we know that the right ventricle pumps blood to the lungs, where oxygen is added via microscopic air sacs to red blood cells in the lung’s capillaries. From the lungs, oxygen-rich blood passes through the pulmonary veins to the left heart, which pumps it through the aorta and through smaller and smaller arteries to the rest of the body to meet the body’s metabolic demands. Blood that has delivered its oxygen drains through capillaries into veins and finally into the superior and inferior venae cavae to return to the right heart to begin the cycle anew. Laid end to end, the vast network of capillaries in the human body would encircle the globe. Their total crosssectional area would cover several football fields. Although the pressure in the veins is low, the pressure in the right heart is even lower, and this provides the necessary push to drive blood back to its pump.
The muscular ventricles pump blood by contracting their fibers in response to electrical stimulation. Each muscle fiber is composed of protein filaments that are stimulated by electrical current to slide past one another, thus allowing the organ to squeeze and then relax, emptying and filling, in repe
titive fashion, billions of times over the lifetime of the animal. The pressure the heart generates is the highest of all the organs, propelling blood through an immense array of arteries that get smaller and smaller, branching like twigs to nourish every cell in the body.
Blood circulates in one direction only. Backflow is prevented through one-way valves. When a valve does not close properly, it allows blood to flow in the opposite direction, a useless expenditure of energy. If a valve does not properly open, it limits the flow forward. In both cases, circulation is impaired. In an indelible pearl of wisdom, our anatomy professor told us that a cardiac anomaly can sometimes cancel another anomaly, if only incompletely. For instance, if a valve does not open, blood must find a path around the obstruction. Such a detour—a hole between chambers, for example, or an anomalous connection—can have devastating consequences in an otherwise normal heart, but in a diseased heart it may actually attenuate the pathology. In the human heart, he said, two wrongs can make an imperfect right.
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At the end of that first semester of medical school, on a freezing January evening, we honored a school tradition and held a memorial service for our cadavers on the twelfth floor of the hospital. (Their remains were going to be cremated afterward.) Four long rows of wooden chairs were filled. Lights were dimmed, and candles were lit; the ceremony was grave and ritualistic, befitting the solemn occasion. People stepped up to recite poems they’d written. A chaplain spoke. A few students sang songs or performed on guitar. Our professor, now stripped of latex gloves and blue scrubs and wearing a crisp navy suit, walked up to the podium to deliver a eulogy. “Who were your donors?” he asked us again. Had we taken the time to think about the lives they might have led? By then, we had dissected most of them away, and yet their last act would live on in each of us. It was our responsibility, he said, to ensure their gift—the ultimate gift—had been worthwhile.
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