Six years ago, John Fisher could barely walk up the short flight of stairs to his bedroom.
Now, he's getting ready to run one of the most gruelling marathons in the world along the Great Wall of China.
This won't be John's first marathon. Since undergoing a heart transplant in July 2000, the father of four has completed the Athens, Sydney, Venice and Snowdonia marathons, as well as the London Marathon - five times!
"I've done three London Triathlons too and cycled across Africa, all to raise money for charities like Transplants in Mind," says John, 44. "Organ donation saved my life and I want to do everything I can to help encourage more people to sign up to the NHS Organ Donor Register."
Back in 2000 though, John didn't think he'd be alive long enough to see his 40th birthday. He was 38 and had been diagnosed with an enlarged heart following an operation to repair an aortic valve.
He can still picture the first time doctors at London's Harefield Hospital mentioned the word 'transplant'.
"I felt numb; I couldn't even say the word," remembers John. "All I could think about was my wife Jan and my kids, and whether I'd see them grow up. I went on the waiting list in August 1999; in July the following year, I got the phone call telling me a heart was available."
John owes everything to his donor Steven Tibbey, who died after a car accident. Steven carried a donor card and had talked about his wishes with his family and thanks to his gift, four people got a second chance in life.
"If it hadn't been for Steven I wouldn't be alive today," says John, who lives in Middlesex. "I've got a wonderful wife and four amazing children. My youngest daughter is now 12 and I can dream of walking her up the aisle at her wedding one day because of Steven."
Since his transplant, John has become good friends with Steven's family and a shining example of how transplant recipients can lead a normal and active life.
"Some people think that you're a shadow of the person you used to be if you've had a transplant, but that's not true. Life's there to be enjoyed to its fullest."