He gave her his liver. She gave him her heart.

Heather Krueger donned a gown and was placed in a hospital bed at the University of Illinois Hospital. In an adjoining room, Chris Dempsey did the same.

Whether a blind date, a chance meeting or even a lucky Tinder swipe, every couple has an origin story.

Heather Krueger and Chris Dempsey are no different, but theirs began in a darker place than most: with stage four liver cancer.

Krueger was diagnosed in March 2014.

The prognosis was not good. That same month, she turned 25. She should have been in the prime of her life. Instead, Krueger was confronting her mortality.

Love certainly wasn't on her mind.

Then, in June, the young woman went into liver failure. Without a donor, death was almost certain, and she knew it, could actually feel it.

"I was told I had less than a 50 per cent chance of living more than two months," Krueger told ABC. "It was traumatic."

"By that time I could really feel my body shutting down," she told CBS.

Krueger had no idea what to do. Even though she had "so many people who tested," as she told the Chicago Tribune, there didn't seem to be any donors. As she so simply put it, "It's extremely hard to find a living donor".

She was out of options.

While Krueger was wrestling with the impossible questions of her own existence, Chris Dempsey was putting in his time as a code enforcement officer in Frankfort, Illinois.

One morning, he wandered into the break room at his office and overheard a sad story. The cousin of one of his co-workers was dying. She needed a liver transplant but couldn't find a living donor, and she was too far down on the state's transplant list - she would likely die before one came through.

Dempsey didn't hesitate. Even though he had never before met Krueger, he offered to be tested to see if he was a potential match.

"I spent four years in the Marine Corps and learned there never to run away from anything. So I just said to myself, 'Hey, if I can help, I'm going to help,'" Chris told CBS.

And doing good deeds was in the man's blood - once, when on the job, he met a 90-year-old, wheelchair-bound woman whose house had fallen into severe disrepair. He didn't write her a ticket though he had the right. Instead, he gathered about 30 volunteers and, with materials he managed to get donated, repaired her home.

In this case, he figured he would have wanted someone to step up if the roles were reversed.

"When I heard about her situation, I just put myself in that situation, thinking if this was one of my family members or me, I would want somebody to help me out," Dempsey told Today. "My mum was kind of nervous at first for me. Some people didn't understand why I would do this for a stranger, but as time went on, people changed their tune and thought it was a cool thing I was doing."

So, he went in for the test, still having never met Krueger. She meanwhile had experienced this particular type of disappointment before, so she "didn't want to get too excited".

After all, he needed to have the same blood type, be in good health and possess a similarly sized liver - most people don't line up in all three categories, so they're immediately disqualified.

Heather Krueger's life was saved.

So she just waited.

And one day, her phone began buzzing. It was Dempsey.

They were a match.

He was going to give her a portion of his liver.

She was going to live.

"I got off the phone and ran down the hallway, and my mother and I were both crying our eyes out in disbelief," Krueger told Today. "I had never even met this man before."

A few days later, he treated her to lunch and discussed the process. In addition to half his liver, he told her he, along with his motorcycle club, was going to hold a fundraiser to help her with her medical bills.

"And then he wants to do a fundraiser," she told the Tribune. "It's just unreal."

As the surgery crept closer, the two became friends. In fact, both began to have feelings for each other but didn't admit them at the time, given the strangeness of the situation.

"He had told me at the beginning of everything, 'You owe me absolutely nothing for this. We can go our separate ways if that's what you want,"' Krueger told Today. "It was kind of like, we do have this special bond, but is this just because I'm sick that I'm feeling this way? You had to kind of separate that, but after the surgery, I realised it went beyond that."

On March 16, 2015, only 10 days before her 26th birthday, Krueger donned a gown and was placed in a hospital bed at the University of Illinois Hospital. In an adjoining room, Dempsey did the same.

The surgery took more than eight hours, but it went off without a hitch.

As their livers completely regenerated, their feelings for each other deepened. When they were healthy again, they realised it was love.

One night in December, Dempsey took Krueger to the top of the Hancock Building overlooking the Chicago skyline and Lake Michigan. Then, they took a romantic carriage ride and in that chilly night, Dempsy dropped to one knee.

Earlier this month, the two were married.

"You are the most incredible man I have ever known," Krueger read her vows to the congregation as she attempted to hold back tears. "You believe in me and you make me feel amazing every single day. Because of you, I laugh, smile and I dare to dream again."

In an interview with Today, she said, "I had an angel watching over me."

"I think about all the what-ifs, like the fact that he normally didn't go into that break room for lunch, or that my cousin is a seasonal worker who happened to be in there that day, or whether someone else would have come forward, and would it have been in time?" Krueger said.

Added Krueger, "I think first of all that it shows everyone, when all you hear is negativity, that there really are sincerely true, kind people out there."