With every beat of his new heart and every breath that flows into his new lungs, 8-month-old Jack Palmer is rewriting what's possible for babies with severe birth defects.

"Baby Jack" is a marvel of modern medicine and moxie after becoming one of the youngest people to have a heart-lung transplant. There is no medical textbook for this and no telling what his future will bring. But the boy who wasn't expected to live more than a few days after birth is used to beating long odds.

"We just live each day as if it might be our last and we don't know what tomorrow brings," his mom, Tiffany Palmer, said. "We cherish every moment."

Jack was born Jan. 16 with an underdeveloped heart and damaged lungs. Many babies in his condition don't even make it to birth, much less live outside the womb. But surgeons at St. Louis Children's Hospital agreed to try the double transplant — a Hail Mary pass of a procedure that only 19 others younger than 1 have had.

His father, Chuck Palmer, is an air ambulance paramedic, and Tiffany is a neonatal intensive care nurse, so they understood it was a long shot. But they also knew it was Jack's only shot.

"Walking into that unit that day the entire staff was just ecstatic because Jack was up for a transplant and they had accepted organs," Chuck said. "[But] we didn't know if it was going to be our last day with him or if it was going to be a miracle that day."

Cardiothoracic surgeon Pirooz Eghtesady had done heart-lung transplants before, but never on someone Jack's age. Jack also needed a reconstruction of the arch where his aorta, a major artery, connected to his heart. Eghtesady had done that complex procedure before, but never in combination with a heart-lung transplant.

"I knew it was a high-risk operation, but at the same time the flip side of it was pretty obvious too," Eghtesady said. "Meaning that if we didn't operate on him, if we didn't do something, he wasn't going to live."

Jack had hypoplastic left heart syndrome, a congenital birth defect in which the side of the heart that pumps blood to the rest of the body doesn't develop properly. The syndrome is responsible for 23 percent of heart-related deaths in children younger than 1. And Jack also had an intact atrial septum, which means his heart was missing the hole that allows oxygenated blood to travel to the left side and be pumped to the rest of his body.

Only about 6 percent of babies are born with both conditions, according to the Society for Cardiovascular Angiography and Interventions.

Jack was the youngest person in 10 years to have a successful heart-lung transplant in the United States. No infant has survived for a full year after the procedure, experts say. But months later, Jack can now roll onto his side, hold his head up and sit up with a little help. Minor milestones for most babies his age, but incredible gifts for Jack's family.

Eghtesady said he and his team are already writing up a case study of the little boy from Kansas City who beat the odds just by breathing.

"The main message that really Jack offers is a glimpse of hope for these babies," Eghtesady said. "Hopefully there will be some degree of paradigm shift and more people will consider heart-lung transplants as a therapy for these babies who otherwise have dismal outcomes."