Knowable Magazine · The heart of invention

The heart of invention: Replacing or assisting the human heart with a machine would save countless lives. But the quest to build an artificial heart has had many gruesome missteps and caused researchers to reimagine how to keep our blood flowing.


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Introducing the Knowable podcast. What are the limits to what’s knowable — and how does our thinking about big questions in science and technology evolve over time? Take an audio journey with Knowable Magazine from Annual Reviews as we explore puzzles as diverse as the existence of black holes and how to build an artificial heart — with plenty of surprises along the way. More episodes


How do you engineer something, when nature has already come up with a solution? How carefully do you follow that tried-and-tested design? And what can you gain by moving away from nature’s influence, and reinventing the wheel?

This is Knowable, and I’m Adam Levy.

You already know what part of the body this podcast is about. And you know what that part of us does. The heart pumps blood around the body. It has four chambers. The smaller right side pumps to the lungs, and the left to the rest of the body. We know what a heart looks like, what makes it tick. So perhaps creating an artificial heart sounds somewhat straightforward. Copy nature’s design, but with artificial materials. Well, the reality has been anything but straightforward.

Marc Simon: “This is really one of those fields that is an incredible journey through history. It’s a real lesson in human persistence.”

This is physician Marc Simon, who’s based at the University of Pittsburgh Medical Center in the US. The journey hasn’t just been defined by its challenges. It’s emotionally significant in a way that few other areas of medicine could be. After all, this is our hearts we’re talking about. Here’s Sharon Hunt, a physician and cardiovascular medicine researcher at Stanford University.

Sharon Hunt: “I think specifically with transplantation of the heart, which as we all know is the seat of the soul, has always been somehow emotionally more significant than putting in a kidney or a pancreas. You just don’t think about kidneys; you just go pee every day.”

But we’ve skipped a beat. Why would you want to create an artificial heart in the first place? Well, because our hearts sometimes can’t keep ticking. Cardiovascular disease remains the most common cause of death in the United States, affecting about one in nine.

When retired historian Else Hambleton was 70, she was in and out of hospital. She was suffering from extreme heart failure after spending over half her life struggling with heart issues.

Else Hambleton: “It can be psychologically really scary when your heart is doing ... when your pulse is really fast and it’s doing things you don’t want it to do. I was told I had about six months to live.”

For many patients with heart failure, a heart transplant is the only option. But this is no easy fix. The body can reject a foreign organ. To combat this, patients have to take drugs to suppress their immune systems, weakening their defenses for infections. And this is if patients can get a transplant in the first place. The demand for healthy hearts far outstrips supply. In the US, the waitlist is around twice as long as the number of available organs in a given year. Here’s cardiologist Haider Warraich of Brigham and Women’s Hospital and VA Boston Healthcare System, both in Boston, US.

Haider Warraich: “It’s not something that you can mass-produce in a factory. It’s something that even to this day is extremely rare to come by, it’s one of the most precious resources on Earth.”

But what if doctors could mass-produce another option? What if a human-built machine could take on some, or all, of the heart’s job while a patient waits for a transplant? What if a machine could even be a permanent alternative to a biological heart? Well, these are questions that doctors and engineers alike have been asking for decades, in a quest to extend the lives of patients with the most severe disease.


In 1954, the Annual Review of Physiology published a review, titled simply “Heart.” In it, a passage on treating heart malformations mentions in passing:

In this connection we are not forgetting the unpublished case of Gibbon who operated on a seventeen year old girl using an artificial heart with very good results.

This seems like a pretty dramatic development to be mentioned as an aside. In fact, this “artificial heart” was used to keep a patient alive during surgery, bypassing her heart and lungs and delivering blood to her body. For 26 minutes, Cecelia Bavolek completely depended on a machine to keep her alive. A significant step to be sure, but a long way from a permanent artificial heart.

Eleven years later, in 1965, another review was published with the same name, in the same journal. It noted the development of an artificial heart, stating that:

Twenty-one implantations were reported with survival times from one to nine hours.

Survival times of just one to nine hours. These repeated, disastrous implantations may sound horrifying, but these implantations were in dogs, not people, though that’s rather unclear in the review.

So what did these early mechanical hearts look like? Well, not too unlike a heart itself.

Marc Simon: “So the first thought was, ‘OK, let’s try to make a mechanical device that mimics the heart.’ That doesn’t sound particularly tough, the heart’s a pump, we have lots of experience building pumps. Air was used to displace a fluid sack, essentially, that would fill and eject with blood. If you were to look at them now, you’d say, ‘Gosh, you’re not putting that thing in me!’”

You really would. The most notable device of the late ’60s looks as much like a piece of an aircraft as it does a part of the body. This horrific heart is composed of large tubes and chambers, fashioned from fabric and plastic, and pneumatically pumped. But, somewhat shockingly, this device was implanted in a patient. In 1969, 107 days before a human would set foot on the moon, a human also successfully received the first artificial heart. Well, “successfully” might be a gruesome overstatement. The patient, Haskell Karp, was kept alive for less than three days on the artificial heart, and just two more after receiving a transplant.

Haider Warraich: “You know, it did not work for many reasons because there were so many moving parts, there was so much risk of blood clots. It was really a disaster. And it was a disaster because we were trying to use technology to replace the heart in the image of the human heart.”

But this image persisted. Nine years later, in 1978, a review in the Annual Review of Medicine, titled “Cardiac Assist Devices,” took stock of progress. The review mentions a number of challenges, such as infection and how to power these devices.

Several power sources have been considered for artificial hearts... Nuclear-powered artificial hearts are currently under development in a number of centers.

Yes, you heard that right: a nuclear-powered heart. Using nuclear power for an artificial heart may seem a radical suggestion, but this was a proposed answer to a question researchers are still asking today.

Marc Simon: “The idea of what would be the power source and what would be the longevity of these devices, are all concepts that really go back in history to a lot of the earlier work.”

The review also brings up a now common medical concept: The left ventricular assist device, or LVAD. Instead of replacing the heart in its entirety, an LVAD would support the left side of the heart to pump blood around the body. At the time, these devices still consisted of a collapsible bladder, mimicking the heart itself. The review states that these machines appear...

… to be the device that is … ready for clinical trial on a large scale.

But for Sharon Hunt, who we heard from earlier, those early LVADs still seemed a long way from being able to save patients’ lives.

Sharon Hunt: “One of the first pulsatile LVADs, they were developing that in the lab down the hall from my office. And I got to know the guy who was developing them, and he was absolutely rabidly in support and felt they were going to change the world. I thought he was a wide-eyed optimist.”

Then, in 1982, the possibility of completely replacing the heart with a machine exploded into the news.

In a 12-hour operation, doctors at the University of Utah Medical Center implant the first permanent artificial heart in the chest of a 61-year-old retired dentist from Seattle, Washington.

This was a concerted effort to implant a mechanical heart in a human for the long term. The effort was a phenomenon. All eyes in the US and beyond were watching.

He’s breathing on his own and has spoken his first words since surgery. “He wanted a glass of water.”

And there was a lot to see. The patient, Dr. Barney B. Clark, survived for over 100 days with his new mechanical ticker, the Jarvik-7. But he also suffered. While this was certainly a far greater success than the effort of 1969, Barney Clark was permanently connected to a loud washing-machine sized air compressor. This kept his new heart beating, but it also prevented him from ever leaving the hospital. And the artificial heart caused a host of complications. These included physical, such as kidney failure and infections, and neurological problems, from memory lapses to seizures. Here’s Marc again.

Marc Simon: “That may nowadays seem pretty horrible, but this was an incredible step forward, and beyond that, we learned a tremendous amount.”

Other patients followed, with varying degrees of success. But as time ticked forward, so did ideas about how machines could replace the function of the heart.

Marc Simon: “Thoughts began to move towards ‘Do we need to be exactly replicating a heart? Can we think about other types of pumps that we use in other types of applications all the time?’ ”

An article published in the Annual Review of Fluid Mechanics in 2006 takes the pulse of progress. Titled “Experimental Fluid Mechanics of Pulsatile Artificial Blood Pumps,” it details the technical, physical challenges of building a pulsing machine — heart-like in appearance, or not. It states:

Work in this important area seems likely to continue for a long time.

In other words, pulsing blood pumps aren’t easy things to get right. But then the review concludes with...

A good deal of effort is currently directed toward the development and testing of rotary blood pumps including axial and centrifugal flow assist devices.

Such rotary pumps are a long way from a heart ventricle — an electrical current causes a rotor to spin and continuously move blood around the body. This is in stark contrast to pulsatile pumps, which repeatedly fill with and then eject blood, in the same style as our hearts. So what led scientists to this new form — a radical departure from the heart’s design?

Sharon Hunt: “The older pulsatile devices had lots of parts; they were complex little machines. And when there are lots of parts, every part has the ability to go bad and break. The bottom line is these newer continuous-flow devices work better.”

Both options were still very much on the table into the 21st century. A 2008 review coauthored by Marc Simon, who we heard from earlier, comments that for assist devices supporting one side of the heart...

Adverse event rates may be lower with continuous flow devices… however, experience with these devices is still considerably less than pulsatile devices.

This review is titled “Current and Future Considerations in the Use of Mechanical Circulatory Support Devices”and was published in the Annual Review of Biomedical Engineering. Left ventricular assist devices (LVADs) are designed to act in parallel with the heart, rather than replace any part of it. They effectively act as a total bypass for the left ventricle, so that some (or all) of the pumping of blood to the body is carried out by the machine. The review points out that by this time, “total artificial hearts” to replace the entire organ...

… are used more sparingly

Continuous-flow LVADs got a major boost of publicity soon after. In 2010, former Vice President of the United States Dick Cheney became the proud owner of such a device. His heart pump would be the subject of plenty of media attention. Here’s Cheney in 2011:

Dick Cheney: “For the past year-plus now, I’ve been living with this device implanted in my chest. So far so good!”

Cheney’s successful stint with his LVAD saw many new patients requesting the so-called “Cheney Pump,” and over the years an increasing number of patients have received these types of devices. If you saw Cheney’s model, the Heartmate II, lying on a desk in front of you, you’d be more likely to identify it as some kind of snorkel than a mechanical heart. The pump itself is around the size of a D battery, with inlet and outlet tubes either side.

Else, who we heard from earlier, received her LVAD about five years ago. At that time, she was 70 and couldn't get a transplant.

Else Hambleton: “I had a marriage, I was happy, and I had a life I really liked and I wanted to keep it going. And the LVAD was presented to me and I really embraced it gladly. I was just so grateful to have a way of staying alive.”

The idea of supporting the heart with a machine has gradually become more mainstream, maybe even mundane. But due to their continuous-pumping design, patients with LVADs generally differ from the rest of humanity in a pretty fundamental way.

Haider Warraich: “They don’t have a pulse! So, you know, if I see someone who falls unexpectedly, the first thing a physician or an EMT or nurse would do is feel their pulse, and if they don’t have a pulse maybe start chest compressions. But, well, these patients don’t have a pulse!”

For Haider, this missing heartbeat begins to stretch what it means to be human.

Haider Warraich: “It’s a remarkable journey. I consider it one of the first steps in trans-humanism. A lot of times when these patients get sick they don’t need a physician, they need an engineer to come fix their pump.”

For Else, though, the peculiar reality of living with a pump in her chest and an altered pulse is nothing compared to what she went through before.

Else Hambleton: “So there’s something comforting about a machine doing the work for me. That’s the thing that is hard for someone who hasn’t experienced heart failure to understand, is that this is so much better than heart failure.”

Over the last decade, the devices, which lie inside the body — along with their external controllers and battery packs — have shrunk substantially. Some LVADs are now around the size of a single AA battery. This not only makes them more convenient, but also means that they can be implanted into smaller people. In other words, they can serve women just as well as men, and are increasingly able to save the lives of children.

Sharon Hunt: “Oh, there’s been a terrific amount of progress, more than I would have foreseen looking at those rather, now in retrospect, primitive devices back when I started looking at them. I would love to see, and I hope to live to see, the day when they won’t require all of this external baggage, if you will ­— literally baggage — to have to carry around with them all the time.”

The most notable part of this external baggage is surely the batteries. LVAD recipients have to wear these at all times, often in some kind of harness or belt. And of course, unlike a cell phone, a dead battery means far more than inconvenience. It can be a matter of life and death. And so spare batteries need to be charged and at the ready at all times.

As well as sometimes feeling self-conscious about her LVAD, Else can find the physical reality of dealing with her device challenging.

Else Hambleton: “I don’t think I understood at the time what, some of the time, what some of the drawbacks might be. I find that the batteries I have to wear are very heavy. And I think I’m starting to stoop a bit because of the weight of the batteries over five years.”

Today some 2,500 patients receive LVADs every year in the United States alone. For most, these are a bridge to keep them ticking — figuratively, not literally — until a transplant becomes available. But for some, these mechanical blood pumps aren’t a bridge but a destination in their own right. This may be because patients weren’t able to have a transplant, as was the case for Else. Or simply because they are happy with their pumps.

Marc Simon: “I have a patient who has probably had a device almost 10 years now. He’s had a child and he says, ‘You know what? I really don’t want a transplant right now.’”

While we’ve come a long way since the bulky, unsettling devices of the mid-20th century, today’s machines are still far from perfect. For one, they still need a power source outside the human body. Sure, that power is now provided using thin electrical wires rather than big pneumatic tubes. But even a wire crossing the skin can pose a serious risk for infection. In the future, wireless charging may help mitigate this risk. But still, these machines can also increase the danger of blood clots. At its worst, this can cause people to suffer from strokes.

Sharon Hunt: “There’s nothing as devastating as having a perfectly, normally well-functioning LVAD and a patient is suddenly stroked out and has no quality of life. There’s nothing worse than that. And reducing the risk of strokes is one of the major goals of developments in the field.”

On top of this, left ventricular assist devices, as their name suggests, only assist the left ventricle. For many patients the smaller right side of the heart — responsible for pumping blood to the lungs — also needs support. This means that, after all these years, researchers are still investigating machines to completely replace the heart. These “total artificial hearts” still mimic biology’s pulsing example but have progressed a long way in the past half-century. One device, for example, led to no detectable blood clots in almost two years of operation across a small group of patients. But it remains to be seen whether they can leapfrog LVADs to become the major mechanical implantation to treat heart failure.

The journey to prolong our lives with artificial hearts has been marked by major milestones — be they the sensational implantations of the early 1980s or the normalization of an LVAD through a vice president. But the progress has been gradual, continuous, and not always positive.

Haider Warraich: “But it’s not happened because of any one breakthrough, it’s really been incremental and a lot of it has been trial and error. A lot of it has been that people had ideas, they ended up implanting it in people with advanced heart failure and then saw how those patients did.”

The body presents us with the perfect prototype for building a blood pump. But if you think you know what an artificial heart should look like, you might have been misled by biology. By avoiding going along with the beat of nature’s drum, surgeons and engineers have saved many thousands of lives.

Marc Simon: “All throughout the history of medicine, the human body has been the inspiration for everything. So I don’t think we would be anywhere without that inspiration. What we see with human ingenuity is that we can then take a step away from that and then move in completely different directions.”

Else Hamberton: “I mean there are frustrations, there are times when I’m really nervous about the way this thing is working. But it comes down to I’m alive. And that’s everything.”

Make sure you’re subscribed to Knowable on your favorite podcast host. Then you’ll be sure to catch our next episode looking at the soaring history of solar power. After all, if a novel technology really is novel, will researchers ever really know how it might fit into the world in the coming years or decades?

“That’s kind of where solar was. It was considered to be, you know, a very advanced kind of far-out technology.”

Catch the episode, from tomorrow. If you liked the show, why not drop us a blood-pumping review on your podcast provider? And drop us an email at [email protected] if you have any feedback or thoughts on the show.

This podcast was made by Knowable Magazine from Annual Reviews, a journalistic endeavor dedicated to making scientific knowledge accessible to all. Through smart storytelling and sound science, Knowable aims to build understanding and fascination with the world around us. Knowable Magazine is free, and always will be. Read more at 

In this episode you heard from Else Hambleton, Marc Simon, Haider Warraich and Sharon Hunt. There were also quotes from five papers: Pierre Soulié, 1954; Edward Hawthorne, 1965; John Lamberti and Leon Resnekov, 1978; Steven Deutsch et al., 2006; and Marc Simon et al., 2008. I’m Adam Levy, and this has been Knowable.