Editor's Note: Derek Fitzgerald suffered heart failure as a complication from non-Hodgkin's lymphoma and received a heart transplant in 2011. Last year, he wrote an open letter to his heart donor.

Take what your body gives you. It's good advice for runners of all levels. But for those who have survived a health scare, like me, those words are especially important as I train for the Broad Street Run in May.

One of the most important things that I came to understand after receiving a heart transplant is that I need to seize the day. For me, that means running — completing multiple marathons, Ironman triathlons, and dozens of other events.

Derek Fitzgerald crosses the finish line of the 2015 Ironman World Championships in Hawaii.
Courtesy of Derek Fitzgerald
Derek Fitzgerald crosses the finish line of the 2015 Ironman World Championships in Hawaii.

But what's the best way to start running while recovering from a major medical event? Every case is different, and you should always consult your doctor before beginning an exercise program, but there are some important rules that I have learned that I'd like to share with others.

Rule No. 1: Listen to your medical team. The professionals who know your body will tell you what your boundaries are so you can stay within them.

I take anti-rejection medication at 9 a.m. and 9 p.m. every day to ensure that my immune system gets along with my new heart. Sometimes that means stopping in the middle of a race to reapply sunblock to avoid unwanted side effects from exposure to sunlight. (I buy sunblock by the gallon.) I also avoid many of the common energy bars and gels that are offered to runners during a race because they contain caffeine, another risk of unwanted side effects. And I haven't eaten anything with pomegranate in half a decade.

All this means that I will never be the guy standing on the pedestal but that doesn't deter my happiness when I reach the finish line. My care will always come first, competition comes second.

Rule No. 2: Don't run too fast. It's very important to listen to your body and do what it's telling you.

For me, that means listening to my heart – literally — by wearing a heart rate monitor.

It typically takes five years for new nerve connections to form after a transplant, so I take longer warm ups and cool downs than other runners so my heart has more time to get the message. And if I can feel my heartbeat pulsing in my ears during the race, I know that means I need to throttle back.

Set incremental goals and take your time building towards them. Shorter distances give you the chance to feel your limits under less pressure. If you want to run a 10-mile race like the Broad Street Run, you must first start with a 5K or a 10K. If you're looking for a short distance race to run, I recommend signing up for Gift of Life's Donor Dash to support organ donation. This year's 5K and 10K runs are on Sunday, April 15. If you are registered for Broad Street, the Dash is a great opportunity to practice an urban race.

Rule No. 3: Don't go too slow. Remember that your body is capable of amazing things and do not assume you're too fragile or broken to try.

My doctors were amazed when they saw my nerves start to form connections with my new heart after just one year. They credited my exercise regimen for boosting my recovery.

The point of all this is not to run marathons or triathlons, but to invest in an active lifestyle. Walking around the block with your family or friends is more important than competitive running. It takes time to get into the rhythm. The benefits aren't always immediate, but they are immeasurable.

Rule No. 4: Run for a reason. When you're feeling tired and you've still got three miles to go in a 10-mile race, motivation matters.

In that respect, I couldn't be more fortunate. There are 115,000 people on the organ transplant waiting list in the United States. Every day, 20 people on the list die waiting. I can't express my gratitude, or put into words the feeling of looking into my 4-year-old daughter's eyes and knowing what I might have missed.

When you're alive because someone else's heart is beating in your chest, you have some extra motivation to get off the couch. After my transplant, I made a commitment to honor my donor's gift by making the most of it every day. When I lace up my shoes and hit the road, I always think about who I'm running for.

I hope you will consider passing the baton. It only takes a few moments to become an organ donor and save lives. Register at donors1.org/registry

Fitzgerald's charity, The Recycledman Foundation, helps people who have experienced significant health challenges to improve their quality of life and become more active. He lives in Doylestown with his fiancée and daughter, Emma.