The catalyst: Donald Arthur, a retired bookkeeper, suffered from multiple health concerns, smoked, drank heavily, and didn't watch what he ate. His careless habits as a young man contributed to serious disabilities as he aged: His heart became dangerously enlarged, and later he was diagnosed with cardiomyopathy. In the spring of 1996, doctors gave him a grim prognosis: Without a heart transplant in six months or less, he would die.

On August 2, 1996, he got his second chance. Arthur received a heart from Fitzgerald (Poochie) Gittens, a 25-year-old Bronx man killed in a horrific case of mistaken identity. Following the successful transplant, Arthur started exercising and joined the Achilles Track Club, a group of mostly disabled runners. Dick Traum, the club's president, nudged Arthur to think about the New York City Marathon.

Arthur, who had never been interested in running, was dumbfounded. "I thought he was absolutely crazy," he recalls. "A marathon? No way!"

The act: Arthur stepped out of his comfort zone and "ran" his first marathon in New York 15 months later. "That's when I began my first journey of 26.6 miles," he says with pride. "I was moved that in my darkest time, others believed in me when I didn't believe in myself. God gave me a second chance. I intend to use it to spread hope." He had moral support: Gittens's brother Mack joined him in that first marathon, and the donor's mother was waiting at the finish line to hang medals around their necks.

Arthur was determined to complete one marathon in all 50 states to honor Gittens and to raise awareness about organ and tissue donation.

Strictly speaking, as a heart transplant recipient, Arthur speed-walks the marathons. It takes him 8 or 9 hours to cover the distance. A host of pre-existing conditions have slowed him down. In 2000, he underwent treatment for prostate cancer.  He also had hernia surgery in 2008. Then he experienced crippling back pain until he had spinal surgery in 2009. Recently, he was diagnosed with mild emphysema. Still, he is determined to meet his 50-state mission.

"Because of my transplant, the first few miles are drudging. Sometimes it's hard for me to breathe with my emphysema. My mind plays games on me and says, 'What the hell are you doing?'" Arthur says what keeps him putting one foot in front of the other is the new heart beating inside his chest. "I can do it," he chants. "I focus on my donor family and what they've done for me."

"When I'm running, I say there are two of us running. [Poochie] is there in spirit, but it's just one body."

The ripple: Fifteen years since his heart transplant, Arthur has logged 46 marathons in 33 states, leaving 17 to go.

Arthur's mission to marathon across America proved to be both a personal and professional goal. One of his most memorable experiences: carrying the 2002 Salt Lake City Winter Games Olympic torch through the streets of New York.

He is the co-founder of Transplant Speakers International, an organization that trains donor recipients to share their stories to raise awareness about organ and tissue donations. Arthur speaks at several organizations and local high schools. Thousands of people, both adults and students, have been inspired by his message. "I talk from the heart. I have no problem crying in front of them. Many kids opened up to me, wrote me letters, and met with me to tell me their problems, things they should never have to encounter," says Arthur. "They tell me how I've inspired them to get their lives back in the right direction."

In a heartfelt letter, one student wrote: "I am writing this simple note to thank you for changing my life. I left my school crying. You blew me away, I was so shocked that you were faced with so many hardships. Always educate kids my age, I know that sometimes we act all tough. But truly we are just waiting for that one person to open us up. I am planning on becoming an organ donor because of your magical words of inspiration. You changed my life and even though I don't know you, I feel as though I've known you forever."

Another student whose grandfather is battling cancer shared: "Hearing you speak to my class Tuesday made me realize that no one knows or is guaranteed tomorrow. You speaking to us made me think about the people I need to start spending more time with.  I have a grandfather who I really love, and he is going through radiation. I realized I'll never know if he'll be here tomorrow or a week later, I have to spend more time with him."

Adults have also been touched by Arthur's story, and many have become organ donors. Life-saving stories continue to ripple in. After speaking to a group of nurses at a hospital in the Bronx, Arthur said: "One of the nurses did not have a favorable opinion on organ donation. I was later told her son was involved in a motorcycle accident, and he was declared brain dead. I was later told that because of my having shared my story she donated her son's organs and saved several lives."

Arthur also volunteers with the New York Organ Donor Network, New York Blood Center, and the Minority Organ Tissue Transplant Education Program.

--Toan Lam

Want to be an organ donor?  Get more information here at www.organdonor.gov