Editor's note: Doylestown resident Derek Fitzgerald has survived non-Hodgkin's lymphoma and the resulting heart failure, thanks to a 2011 heart transplant. Now, he is a triathlete with multiple Ironman races to his credit. If he could talk to the person who gave him a heart, this is what he would say.

Something horrible happened to you, and when it was over so was your life. But your story didn't stop there, and neither did your heart. I'm here to tell that story — as the world's only cancer-surviving, heart-transplant receiving Ironman — because that's when you and I met.

It was early 2011, and everyone was still recovering from celebrating the New Year. At some point you had checked off the "organ donor" box on your driver's license, and maybe you didn't even think that much of it. But as we celebrate Donate Life Month, I want everyone who makes that decision to understand what your selflessness did for me.

I was 37 years old, from the Philadelphia suburb of Harleysville, and had spent the previous eight years fighting for my life. First it was cancer, but the chemotherapy damaged my heart, causing a type of heart failure called dilated cardiomyopathy.

As my heart became progressively weaker, I became a prisoner inside my own body.

For years my last thought as I went to sleep was to wonder whether I would wake up. Living under the motto "Hope for the best and prepare for the worst," I was thankful each time my eyes opened. Eventually, I was awake only a few moments each day. My family would sit beside my bed, hold my hand and cry.

On the last day of your old life, I was propped up in a hospital bed at the University of Pennsylvania, where I'd been for a week, knowing only that change was coming soon.

I was awake when the transplant coordinator rushed into my room. She told my family and me that they thought a heart had been found. I looked around the room at the tears of happiness that flowed and I thought of you and your family at that moment, and how different that scene must have been.

Your heart was flown in by helicopter as I was wheeled to surgery. Despite having consent from you and your family, nobody knew whether we were truly compatible until your heart was placed next to my opened chest. It wasn't until I woke up and heard your heart thumping, strong and healthy, pounding its rhythm into my ears, that I started to understand: I was no longer just "me"; the only reason I was alive was because I was "us."

I immediately made two promises: I vowed to become the best custodian to your heart that I could be, and to live as if you were watching. I made it a point to work less, laugh more, and say the words "I love you" more frequently.

During cardiac rehabilitation, I "kicked the tires" to see what my body could do. Each day, I would challenge us a little more, trying to be a little bit faster, a little bit stronger, and each day you responded.

Your gift made it possible to run our very first 5K at the Travis Manion 9/11 Heroes Run in Harleysville — just eight months after surgery. Since then, we've crossed the finish line of more than 80 endurance events. We've run half-marathons, marathons, and became the first cancer-surviving heart transplant recipient to complete the full 140.6 mile Ironman triathlon. We even crossed the United States on a bicycle, from the Pacific Ocean to the Atlantic.

We created RecycledMan.com to celebrate our intertwined destinies, and to raise awareness of why more people need to become organ donors. We achieved both goals on April 1, running the Ironman 70.3 in Oceanside, Calif., and we will do it again at the Delaware Valley Duathlon on April 30.

Every day of the last six years has been a gift, but without a doubt, the very best gift has been fatherhood. Your selflessness and generosity saved my life, and made possible the little miracle who calls me "Daddy."

Both our stories could have ended six years ago. My body may be the vehicle, but I know that nothing is possible without your engine. Words will never be able to express my gratitude, but thank you, my friend — for my daughter, for me, for us … thank you for everything.