After eight years of training, Dr Maureen McKiernan made her debut as the lead surgeon on an infant heart transplant – an operation on the edge of what’s possible.

On the day she transplanted the heart of a 6-month-old
infant, Dr Maureen McKiernan awoke, as always, to a 4.30 alarm.

In the dim light of her apartment, she moved through her morning routine: a spin on her rowing machine, some mat Pilates, a hot shower, the usual breakfast of yoghurt and granola. It was a practical meal – one she could eat half standing, spoon in one hand, phone in the other, scrolling through her upcoming cases.

After breakfast, she took the A train to NewYork-Presbyterian Morgan Stanley Children’s Hospital in northern Manhattan. There, in a thicket of acronyms and surgical jargon, McKiernan typed up the 16-point procedure she would use to save baby Luna, whose new heart would be flown in that night.

Step 9: Plane lands –> cross-clamp, cardiectomy

They would keep Luna alive with a mechanical pump as they cut her heart out. When the donor heart arrived, McKiernan would have 90 minutes to get it beating inside her.

Every year, doctors in the United States perform about 100 infant heart transplants, an operation on the ragged edge of what’s possible. They remove the heart from one baby whose life has functionally ended, pack it on ice and then coax it back to life in another. The margin for error comes down to minutes, stitches and a few fragile millimetres.

Seven in 100 infants who receive new hearts die before they can be discharged from the hospital, according to a 2022 study.

For McKiernan, 39, only a month into her job at NewYork-Presbyterian, this case was a milestone: her first heart transplant as the lead surgeon and her first ever in an infant. As a trainee, she had helped take out an infant heart, but this would be her first time putting one in.

That evening in September, with Luna prepped in the operating room, McKiernan paced the floor, checking that the surgical team had what it needed, that no piece of tubing or suture would go missing at the wrong time. She reviewed her plan once more and then closed her eyes and visualised the procedure.

“The last thing you want is to freeze and be like, ‘What do I do next?’” she said later. “I’m always worried: Am I going to harm this patient somehow?”

Around 8.30pm, the call came: the donor heart was in good shape, and it was time to start cutting. McKiernan slipped into the bathroom one last time – a small, practical ritual. Looking in the mirror, she took a breath and then headed back to scrub in.

The operating room was a humming command centre with stainless-steel walls, circular LED lamps hanging from the ceiling and screens flashing with vital signs. Luna lay still in the centre while about a dozen masked health care workers shuffled around: nurses sorting clamps, scalpels, sewing needles; anaesthesiologists keeping her stable and asleep; perfusionists ready to operate the heart-lung machine. Carts, pumps and monitors pressed in from the edges, with bags of fluid, medicine and blood hanging from IV poles.

On one wall, a series of TV screens glowed with the hospital’s motto: “STAY AMAZING”.

Wearing tan clogs and a Kansas City Chiefs surgical cap made by her mother, McKiernan seemed relaxed but focused. (With permission from the hospital, I changed into scrubs and observed from a corner.)

Luna was nearly buried under blue sterile drapes. Only her chest remained visible, a small rectangle flooded with light and lacquered orange with antiseptic. The scene was almost peaceful until McKiernan moved to slice through Luna’s small breastbone so that she could remove her heart, step one in her plan.

She drew her scalpel down Luna’s chest. The knife elicited a slow ooze of blood, followed by a bright rush of red when McKiernan took a power saw to the bone and cranked apart Luna’s sternum with a retractor. She was careful not to cut into the heart; the smallest slip would unleash catastrophic bleeding.

McKiernan then used scissors and a cauterising tool to cut away layers of fragile, overgrown scar tissue left behind from previous operations. She could just make out the heart beating underneath.

McKiernan grew up in Kansas City and was well into her 20s before she found her way into medicine.

In school, she was “very shy and reserved,” McKiernan said, but she always had a deep interest in science. She and her father would build weather-themed projects for her grade school science fairs; growing up, McKiernan wanted to become a meteorologist.

“I thought that she would be in the sciences somewhere, but I didn’t anticipate her being a doctor,” said her father, Brian McKiernan.

After college at Kansas State, she chased chemistry into a doctoral programme, only to drop out and move back home because she felt the work was too removed from people’s lives.

So with no Plan B, she applied to medical school. McKiernan had been curious about medicine since age 13 when her grandmother was diagnosed with cancer. She said that she “couldn’t wait to get out of Kansas City,” but after an unsuccessful first round of applications, she ended up at the University of Kansas, 10 minutes from home.

It wasn’t until residency at Emory University that McKiernan first saw paediatric heart surgery. “It was one of the moments where you’re like, ‘Oh, my God, this stuff is so cool,’” she said. “I loved how complex it was, and how mentally stimulating and challenging it was.”

In August, after eight years of training, she joined the faculty of Columbia University, practising at NewYork-Presbyterian, the nation’s busiest paediatric heart transplant centre. In a subspecialty with vanishingly few jobs, the hospital was the only one to offer her a spot.

McKiernan was ready to swap out Luna’s blood. Organ transplants are a con game perpetrated on the immune system: the idea was to trick Luna’s body into thinking the new organ actually belonged to her. However, Luna’s blood type was different from the donor’s, so McKiernan needed to supply blood that made them match. She had never performed an exchange transfusion, so she talked through the steps with her colleagues and brushed up on the procedure the day before.

Standing across the operating table from her was Dr Andrew Goldstone, a veteran transplant surgeon and the incoming chief of paediatric heart surgery. He said later that he was there to advise McKiernan and to “be the best assistant I can be” while she crossed this threshold in her career. “It’s a very stressful time when you’re starting out as a surgeon,” he said.

Goldstone reminded her of the steps they needed to follow and then instructed the OR staff to shut off the pump that had kept Luna alive since her heart started failing months earlier.

McKiernan checked that everyone was ready. “All right, go,” she said.

“Starting the exchange,” announced one of the perfusionists.

“Work it!” Goldstone yelled, his voice cutting through a chorus of shrill alarms as Luna’s blood drained out into a bucket.

“Nothing,” McKiernan said, reading the monitors measuring Luna’s pressure. The new blood wasn’t coming in fast enough. If Luna’s blood pressure didn’t rebound soon, her organs would be slowly starved of oxygen and start dying.

“We’re almost there,” said the perfusionist as the cardiopulmonary bypass machine started pumping in fresh blood. “OK, we’re on bypass,” he added.

“The exchange is done?” Goldstone asked the team, a bit incredulously, a bit jokingly. “Without any issues?”

Goldstone seemed at home bantering even during serious moments.

“This is varsity stuff,” he added approvingly, using a more colourful word.

McKiernan chuckled but stayed intent on her work. She was too anxious for jokes.

Luna Maradiaga Maldonado wasn’t born sick.

Her mother, Jessy Maradiaga, 22, said her 18-hour labour ended with a pink, squirming baby girl letting loose a full-throated cry. “Everything was perfect,” Maradiaga said.

But when Luna was 2 1/2 months old, Maradiaga noticed she wasn’t eating much and seemed tired. Luna was breathing fast, and her body was cold. Maradiaga and her husband, Gerson, who live on Long Island, took their tiny baby to a nearby hospital, where the doctors saw that Luna’s heart was failing. They didn’t have the tools to save her, so within hours, Luna was on her way to NewYork-Presbyterian, the ambulance flashing its lights, her mother riding along in silence.

“I was overwhelmed, scared, sad and angry at the same time,” Maradiaga said.

The diagnosis was dilated cardiomyopathy: Luna’s heart had thinned and stretched to three times its normal size – too weak to pump blood effectively. Luna was in end-stage heart failure, said Dr Marc Richmond, a paediatric cardiologist at NewYork-Presbyterian.

In that first month, Luna’s heart once stopped for four minutes, she had a stroke, and she endured weeks of nonstop seizures, Maradiaga said. The doctors warned that even if Luna survived, she might not be able to move, walk or talk. She was soon placed on the heart transplant list, where chance held her fate hostage.

In a September 20 post on Instagram, after four months of waiting in the hospital with her daughter, Maradiaga wrote, “Sometimes I just cry because I don’t know what to do to make my baby Luna feel better.”

The call came later that week. “The waiting is over,” Maradiaga wrote. “Our warrior Luna Giselle is going to get her new heart our miracle is here.”

On the day of surgery, she dressed Luna in a Strawberry Shortcake dress and a pink hair bow with hearts. “She’s a fashionista,” Maradiaga said. Hospital staff members added a pair of pink heart-shaped glasses, one lens reading “Luna’s Heart Day,” the other “9/26/25.” Nurses blew bubbles as Luna was wheeled out of the ward.

Heart surgeons are a superstitious bunch, McKiernan said. Say out loud that things are going well, and you invite disaster.

“Heaven forbid you call a baby cute – that’s a no-no,” she said. She wanted to call her parents to tell them about the surgery but held back, worried about jinxing the case.

As the bypass machine took over for Luna’s heart and lungs, it also cooled her body to 90 degrees, slowing her metabolism and buying the surgeons more time to work.

It was time to remove her heart.

With what looked like an oversize metal clothespin, McKiernan clamped the aorta and then used scissors to snip the vessel just below it. Working alongside Goldstone, she did the same to the pulmonary artery, which feeds the lungs, before carefully cutting around the tops of the heart’s two upper chambers.

Goldstone reached his gloves into Luna’s chest and pulled out her failing organ. It was the size of an orange, but hollowed and ballooned out, its walls stretched thin with strain.

Luna lay on the operating table, her chest splayed open, hauntingly empty save for bits and pieces of heart tissue, still fluttering faintly with the last traces of its own rhythm.

“When you look inside the chest and there’s no heart inside, that’s always surreal,” Goldstone said later.

McKiernan was before schedule. The plane carrying Luna’s new heart hadn’t landed yet. She had no reason to doubt it would arrive. But she couldn’t help the nervous thoughts: Planes crash, things happen. What if we don’t get this heart – and we’ve already taken her heart out?

The donor heart had belonged to a baby – just a few months old – who had died hundreds of miles away. It was flown into Teterboro, New Jersey, by private jet and rushed to Manhattan with a police escort, arriving at NewYork-Presbyterian in a white Styrofoam cooler.

The heart was suspended in a tiny life-support pod, the organ bathed in an ice-cold solution.

With Goldstone’s guidance, McKiernan lifted the heart out of the container. Cradled in her hands, it looked like a sickly, mouldy strawberry.

“That is a small heart,” McKiernan said with a sigh.

“Uh oh,” Goldstone said.

“Uh oh,” she echoed, not quite joking.

In most heart transplants, surgeons hook the donor’s two major veins directly to the recipient’s. But with a heart this small, that felt especially risky. So, Goldstone offered an alternative technique, stitching the tops of the heart’s two upper chambers to the remnants of Luna’s, rather than sewing each vein one by one. This is known as a biatrial transplant.

McKiernan had assisted on a handful of such transplants in adults, but never in a child. She said later that she was happy to follow Goldstone’s lead.

On paper, a heart transplant is just a plumbing job, a matter of making four connections and sealing up four seams. But in Luna’s chest, the ends didn’t quite match because her pipes were much larger than the ones in the donor’s tiny heart.

McKiernan had to creep around each circle, stitch by stitch. It was like sewing the top of a big sock on to a smaller one, easing in the extra fabric so that the seam lay flat instead of bunching or twisting.

All of this happened on an unforgiving clock. From the moment the donor heart was cooled and deprived of blood, its cells had been slowly dying. At this point in the operation, McKiernan had about 75 minutes to get the heart in and bring it back to life.

The suture she used was thinner than a hair, and the pipes she was sewing together were paper thin. The last thing she wanted was a strangled connection that choked off blood flow, or a loose stitch that leaked blood once the heart started beating.

“You’re anxious, and you want to rush,” McKiernan said later. “But the last thing you want is to have bleeding behind the heart that you can’t fix.”

By now, the new heart was almost fully hooked up, with McKiernan tending to the final connection.

Around the table, the mood flickered between levity and sombreness, with Goldstone shifting between supportive coach and comic relief.

“Looking good, Billy Ray,” Goldstone said. No one bit, so he supplied the rest himself: “Feeling good, Louis.”

The faces around Luna remained blank. “No, nobody?” he asked.

He appealed to the whole operating room: “Has anybody seen the movie Trading Places?”

McKiernan, anxious and preoccupied with perfecting every stitch, hardly looked up.

With all the connections in place, she reached for the oversize clothespin and eased it off Luna’s aorta. Blood rushed back into the coronary arteries, and Luna’s tiny new heart flushed warm and red.

It began to quiver unsteadily, so McKiernan stitched a temporary pacemaker to its surface to nudge it into a steady rhythm. But after 20 minutes, the heart was still only stuttering along.

“You still have a good feeling about this heart?” McKiernan asked.

Goldstone reassured her; it takes time for a heart to wake up. She knew that, but she worried that they might have permanently injured the heart’s electrical system. Slowly, though, the random twitches began to steady. Soon, almost imperceptibly, the muscle found its natural rhythm – a real heartbeat, pushing blood through Luna’s body.

McKiernan had finished with 37 minutes to spare.

“We didn’t sew it the wrong way?” Goldstone asked, with a smile in his voice.

No, said the cardiologist monitoring Luna’s heart. No, it’s all perfect.

The six-hour operation wrapped up around 2.30am. McKiernan peeled off her gown, pulled down her mask and rushed straight to the bathroom.

Her job was done, but she couldn’t bring herself to leave. “In those first few hours, there’s a lot that could change for the worse,” McKiernan said.

In her office, McKiernan kept refreshing Luna’s medical record, looking for new numbers, new notes, any sign that things were going off track. She ran up to the ICU – once, then again, then again – to make sure Luna was OK and that no one had any questions.

Somewhere in the middle of it all, her hunger hit, so she scavenged a bag of Lay’s and a few squares of chocolate. Around 4.30am, 24 hours after her alarm had gone off, McKiernan finally left NewYork-Presbyterian and headed home. She had trouble going to sleep but managed to get a few hours. By 11am, she was back at the hospital to check on Luna.

Later that day, McKiernan called her parents in Kansas City and told them about her big operation and how well it had gone.

Every heart transplant depends on the loss of a life, advanced medical science and, for the recipient, incredibly good luck. If you followed 100 infants on the transplant waiting list for a year, about 25 would die before they could receive a heart.

But a heart transplant is no guarantee of long-term health. Recipients spend the rest of their days on immunosuppressants, living with a high risk of infection and the perpetual fear that the new heart will be rejected. In the most recent long-term studies of infant transplant patients, roughly half did not make it past 25 years of age.

“This heart’s not going to last forever,” McKiernan said of Luna. “She’s not going to have a normal life span.”

That was the hard reality of McKiernan’s work. But she took satisfaction in giving Luna time she wouldn’t otherwise have had – days not measured in alarms, months untethered from a pump, years no longer living in the hospital.

McKiernan doesn’t see her first transplant patient around the hospital anymore. A week before Christmas, after five months at NewYork-Presbyterian and two months building her strength in rehab, Luna went home.

This article originally appeared in The New York Times.

Written by: Simar Bajaj

Photographs by: Victor J. Blue, Simar Bajaj and Vincent Alban

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