In December 2012, Lisa Swanson's son Levi Schulz died in a car crash aged 18.
Levi's body was kept on life support so that his organs could save others, and three days after the car accident his heart was received by Terry Hooper, who suffered from cardiomyopathy, a heart muscle disease where the organ loses its ability to pump blood.
Swanson and Hooper exchanged several letters and emails in the last few years, but until this month they had never spoken on the phone or met face-to-face.
They finally met at Nebraska Medical Centre in Omaha on 1 April, where Swanson was able to listen to her son's heartbeat.
"It's so nice to meet you," Swanson says to Hooper, 64, in an emotional video of their meeting. "You can't cry though, OK, because then we won't get through this."
Hooper described Levi, whose twin brother, Shelby, accompanied their mother to the hospital, as his "hero".
"There's not a day I don't think of him," he says in the video.
Swanson wept as she listened to an ultrasound of her son's heartbeat, and was later presented with a soft toy that plays the same sound.
She said it was "really good" to hear Levi's heart beat inside Hooper, who wore a T-shirt with the teenager's face printed on it to the meeting.
"It definitely sounds like it belongs there," she said. "I get happiness and sadness all at the same time. Sad that my son's not here but happy that he was able to help Terry."
Matthew Champion is a weekend editor for BuzzFeed News and is based in London.
Contact Matthew Champion at firstname.lastname@example.org.
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