I’m a middle-aged guy with a winebelly who can never find an exercise regimen that sticks, and I still can’t get used to the fact that I have to take a pill every day to lower my cholesterol. At this moment, in fact, I have a prescription waiting for me at CVS which I conveniently keep forgetting to pick up.

In short, I’m not taking the best care of my heart. But after getting to know Shovon Greene and Allison Canfield, I realize just how much I’m taking for granted. Young, vibrant people, they’ve known how fragile their hearts were from the time they were children.

“One thing they’re always saying about Shovon is he’s always smiling,” says Greene’s mother, Octaverie Hall.

His sunny nature is all the more remarkable when you learn what Greene, 19, has been through. He was born with dextrocardia, a defect in which the heart develops on the right side of the chest instead of the left. His heart also had only one ventricle: “I only had half a heart” is his poetic way of putting it.

Other defects were found soon after he was born, and by the time he was 10 he had had six surgeries, including implantation of a pacemaker. At 16, he was given a heart transplant.

His mother happened to pick up the phone in his hospital room at All Children’s when the call came through that a heart had been found. “It was a breathtaking moment,” she says, and remembers throwing open the door, waving her arms, and shouting the news to the nurses.

Greene’s saga has been followed by news media since he was a toddler, and he and his mother are now active in LifeLink Florida, the non-profit organization that supports organ donation, and with the American Heart Association. Greene is studying to be a paramedic at Southeastern College, and has gone on ridealongs with EMS crews as an Explorer with St. Pete Fire and Rescue. He wants to help people the way he’s been helped.

“I know what they’re going through,” he says. “I’ve lived through it.”

Canfield, 35, is also eager to help others; like Greene, she’s an AHA volunteer. The manager of marketing and special events at St. Pete’s Museum of Fine Arts, she says the most important lesson she learned from her experience with heart disease is this: “Pay close attention to your body, and if you are experiencing symptoms that aren’t normal, don’t delay in having them checked out.”

That’s what she did after noticing fatigue last year during a family vacation in New York.

“After getting back from my trip, I was so tired and lethargic that at one point I required a daily nap. I was also having shortness of breath when climbing a short flight of stairs.”

She’d been diagnosed with mitral valve prolapse when she was 11 — a condition in which the valve that separates the upper and lower chambers of the left side of the heart does not close properly — but had never suffered any side effects. She’d made a point of having echocardiograms through the years, however, and in 2008 was told that the valve might one day need to be repaired.

Her excessive fatigue, it turned out, was a symptom of a weakening valve. Her cardiologist confirmed this fall that surgery would be necessary, and in October, heart surgeon Dr. Cedric Sheffield of Tampa General Hospital successfully repaired the valve.

“I didn’t realize how bad I was feeling until I started to feel better,” says Allison, “and he gave me a new lease on life. It took six weeks of recovery time and then one day I just woke up and felt like myself again … but better!”

Greene and Canfield had the benefit of knowing early on that they were at risk. They were literally listening to their hearts.

That’s not often the case with young people, most of whom see themselves as invulnerable. Heart disease is still regarded as an ailment of, well, middle-aged guys. But cardiologist Dr. Chris Wilson of St. Petersburg’s Edward White Hospital has seen “an increasing number of younger and younger patients having complications related to diseases of the heart and arteries.” He also points out that autopsies of soldiers during the Vietnam War found evidence of fatty streaking in the arteries of men in their teens and early 20s.

“You need to start making the right choices early on,” says Wilson, “to prevent the untoward events later on.”

Besides getting familiar with your family history — genetics are a major factor in heart disease — the right choices are simple: Eat right, exercise, and stop smoking. Or better yet, never start.

This one’s close to Dr. Wilson’s heart; he stopped nine years ago, and often brings that up when he’s doing community outreach. “Cutting down never works,” says Wilson. “You have to throw them away. You have to be like Nike and just do it.”

But where consciousness has arguably been raised among young people about the health risks of smoking, the cardiologist sees childhood obesity as just as big a threat, and notes that savvy marketers are using humorous paeans to over-eating the same way they used to make cigarettes seem like innocent fun.

He recalls ads where “you used to see Santa smoking Charlestons.” That would never fly today, yet people accept marketing ploys like the Vegas-based Heart Attack Grill, where if you’re over 350 pounds, you eat for free.

“As laughable as Santa smoking a cigarette is now, some of these things should be equally as laughable — big risk factors unfortunately targeted at younger people.”

That’s where messengers like Green and Canfield can make a difference.

Canfield hopes others will follow her example and listen to their bodies: her symptoms, in a sense, saved her life.

And Greene is not shy about telling friends what heart disease entails, making sure to point out the risks of smoking.

“I usually tell people who smoke at school the side effects. They say, ‘It’ll never happen to me.’ That’s what everybody says who it happens to.”

Right. I think I’ll go make that stop at CVS.