Surgeons trying a new way to save the life of a baby born with half a heart stood over her open chest and waited for the FedEx box.

Doctors in Miami had overnighted two vials of stem cells to the University of Maryland Medical Center. Now the Baltimore surgeons would inject the cells, derived from a donor’s bone marrow, into the tiny, defective heart of 4-month-old Autumn.

The Hagerstown girl was born with an often fatal condition called hypoplastic left heart syndrome, in which the left half of the heart is unable to pump blood. She is the fifth child to get the injections into the working right half of her heart as part of a national study aimed not only at saving lives, but also allowing children with the condition to live more normally.

“Not to be superstitious, but we liked that she was No. 5,” said Wayne Brown, Autumn’s father.

Both Brown and LeeAnn Janes, Autumn’s mother, were born on the fifth day of the month.

“She’s become our Lucky No. 5,” Brown said.

After seeing some promise in trials on adults who have had heart attacks, strokes and other cardiac problems, researchers believed stem cells might benefit children with heart problems.

Autumn Brown is one of 10 babies in the study now receiving cells to check for safety and feasibility. Another 20 will be enrolled at Maryland and other pediatric hospitals around the country. Half will get stem cells, in a trial to determine whether the treatment helps.

Some 950 babies each year are born with hypoplastic left heart syndrome. Left untreated, the condition is always fatal. For now, the lone treatment is a course of surgery developed 30 years ago. It’s performed in three parts: at birth, at about four months and at age two or three.

Even with the surgeries, only 60 percent of the children celebrate their fifth birthdays. Then the overtaxed partial heart fails, necessitating a heart transplant, which brings more risks.

Dr. Sunjay Kaushal, director of pediatric and adult congenital surgery at the University of Maryland and one of the foremost surgeons for hypoplastic left heart syndrome, said Autumn’s general health beyond the condition and her supportive parents made her a good candidate for the stem cell study.

His team of about a dozen arrived early for the surgery, draped blue cloths around Autumn and hooked her up to machines that would at times do her breathing and pump her blood for her. Her chest was reopened along the same several-inch-long line used in her first surgery.

After tThe heart surgery was done, the team waited for the courier delivering the stem cells. The roughly 1.67 million cells had been in a freezer at the biotech company Longeveron and once the liquid cells arrived, they were hurried into the operating room. An examination under the microscope showed they were 77 percent viable, above the 70 percent threshold for use.

A member of the team held up a diagram of a heart for Kaushal, an associate professor of surgery in the University of Maryland School of Medicine and director of pediatric cardiac surgery at the medical center. He pointed to a spot each time he plunged a needle into Autumn’s heart.

If the cells work as they did in Kaushal’s computer models and lab animals during nearly a decade of research, they will boost the strength and longevity of Autumn’s half a heart.

Kaushal said the first four children to receive the cells were faring well. “I think this is game-changing for these kids,” Kaushal said. “I believe these young hearts are going to be the most responsive.”

In a normal heart, the right side of the heart typically has the less stressful job of pumping deoxygenated blood from the body to the lungs. The left side more powerfully pumps the resupplied blood back out to the body. In babies with Autumn’s syndrome, the right side has to do double duty.

The three surgeries changes how blood flows so deoxygenated blood goes right to the lungs and refreshed blood is pumped around the body by the right side of the heart.

Kaushal has been working with Dr. Joshua Hare, founding director of the Interdisciplinary Stem Cell Institute at the University of Miami Miller School of Medicine. Hare formed Longeveron to translate research into medical use. Longeveron, the University of Maryland and the state-established Maryland Stem Cell Research Fund are sponsoring the initial $1.5 million cost of the study.

Longeveron harvested the mesenchymal stem cells from a young adult donor and allowed them to multiply in a culture to produce enough for use in every baby in the trial. These types of cells can become any kind of human cell.

Once in a baby’s heart, Hare said, they can reduce scar tissue, reduce inflammation, promote new small vessels and — perhaps most importantly — stimulate the heart to grow. Her mom sees the stem cells as “creating a super heart.”

Data collected so far on stem cells in adults or children have not convinced everyone of the long-term possibilities. The FDA has approved stem cells only for disorders related to blood production. But the agency has allowed their use in well-reviewed studies, including the heart study.

“My ultimate hope is we can show we can reduce the need for transplants and kids do better, not just by increasing the functioning of their hearts but make them feel better and live longer,” Hare said. “The goal is really to make kids better.”