In Panama City, 7-year-old Mariah York's parents had been trying for a long time to give her a brother or a sister. Last fall, it finally happened.
"What a gift it was, and what a miraculous thing it was that had happened," Tracey York said. "He just lit up a room with a smile."
On a typical day last February, Mariah went to school as Tracey went to her waitress job and her husband, Russell, was working as a cook at Applebee's. Baby Jordan was left with his grandparents.
Roughly two hours later, in the kind of life-shattering accident all parents fear, Jordan suffocated underneath a pillow.
Hours later, doctors told the Yorks that their "miracle baby" -- the child they had tried to conceive for five years -- was brain dead. "There was just nothing that could be done," Tracey said.
They were then asked to consider donating Jordan's organs.
While the Yorks were deciding, the Drapers were entering their seventh month of waiting for an infant heart. It was Valentine's Day, and they were about to be connected to another family in ways neither could have imagined. The Yorks had said yes to donating Jordan's organs.
For Russell York, the decision was a way for his son to "live on" despite the tragedy.
The following day the Drapers received the news that 7-month-old Nick was getting a heart.
"To be quite honest, I was scared," Michael said. "This is the big surgery. This is it. There's nothing bigger."
The surgery was to be performed by Mark Plunkett, a surgeon with a successful track record and a full appreciation of the risks.
"This is someone's little boy. The stakes are high because the rest of his life is hinging on what we do here," Plunkett said.
Just after dawn on Feb. 16, Jordan's infant heart arrived at the UCLA hospital, raced from the airport by helicopter.
In a tense moment, the Drapers walked Nick to the surgery. "You are handing your son over and you don't know the outcome," Michael said.
When the surgeon opened his chest and removed the ailing heart, the defects were instantly apparent. When the healthy heart was implanted, it started to beat immediately. About four hours into surgery, the small heart became sluggish and the heartbeat was erratic. "I was sweating bullets at that point," Plunkett said. "Obviously this was a horrible problem."
"This kid goes through eight months of never going out of the hospital, and you're going to tell me that some other child had to pass away and gives up his heart and then we are going to have a problem now?" Michael said. "This can't be the way this plays out. This is unimaginable."
The doctors told the Drapers the next 72 hours would determine Nick's chances for survival. Immediately after his transplant operation, it was life support machinery -- not his new heart -- that was keeping him alive.
Three days after the surgery, doctors noted a remarkable turnaround. "It was just absolutely amazing to us that the little heart was beating almost normally inside our baby," Nicole said.
"He now has the opportunity to sort of grow and develop normally," Plunkett said.
Now the family waits for a heart for Nate. Doctors first said both boys would need new hearts within three months to six months of birth. Nate is already two months past that deadline.
For now, the Drapers are taking things one miracle at a time. Last Saturday, baby Nick came home with the family to their accommodations in UCLA's Tiverton House, which offers housing to families with patients under the hospital's care.
They remain grateful to the family that enabled this moment.
"We stand in awe of them," Michael said. "And you know little Jordan, you know he saved Nick. And, we'll always, we'll always remember Jordan."
In a highly unusual decision for families on either side of a transplant surgery, the Yorks and Drapers decided to meet in person. Watch these two families, joined by two children, meet for the first time on "20/20."