(CNN) -- Every morning, Christy Farley rises from bed and feels relieved.
"Not a day or minute goes by where I don't think about how lucky I am just to be here," said Farley of Hasbrouck Heights, New Jersey. "I thank God every day when I wake up that I woke up."
Around Christmas time, 24 years ago, Farley's heart was deteriorating.
Farley was 12 and couldn't walk without feeling exhausted. She'd stop to catch her breath after taking a few steps. During gym class, her lips and fingers turned purple from low blood oxygen levels. She often felt listless, and she had chronic bronchitis and respiratory infections.
She had cardiomyopathy, inflammation and thickening of the heart muscle, which makes pumping blood difficult. With her health fast fading, Farley landed on the waiting list for a transplant. In February 1986, Farley got her new heart at the NewYork-Presbyterian Morgan Stanley Children's Hospital in New York.
Pediatric heart transplants, which were pioneered as early as the 1960s and widely performed in the 1980s, are showing better results as medical technology and drugs have improved. Former child patients such as Farley, who received heart transplants, have grown up enjoying stable, long-term health.
A Stanford University study published in 2006 in The Journal of Heart and Lung Transplantation found that 77 percent of pediatric patients who underwent heart transplantation between 1974 and 1993 survived past 10 years.
In the early 1980s when pediatric heart transplantation was still rare, the survival rate was much lower, said Dr. Gerard Boyle, who chairs the pediatric cardiology department at the Cleveland Clinic Children's Hospital.
"At that time, it was still very experimental surgery," Boyle said. "So you didn't take the patients who you thought had some more time. You took patients that you were really desperate with them. So over time, we've learned those are not the best candidates."
In the early 1980s, the one-year survival rate for pediatric cases was about 80 to 83 percent. In recent years, that one-year survival rate has come to 95 to 98 percent, he said.
The life expectancy of someone with a heart transplant is unclear, and it's also difficult to gauge whether organ recipients may need another transplant, experts said. It's a possibility that Farley does not think about.
"I really try to take good care of myself so that doesn't happen," said Farley, 36. "I'm extremely lucky. I don't know how much is luck, compliance or combination of both."
After the surgery, Farley no longer felt constantly fatigued or sick.
"I never knew what it was like to feel good," she said. "It was never being able to do everything someone would normally do. It would be as simple as walking up flight of stairs."
With her new heart, Farley graduated from high school and college, became a nurse and recently gave birth to a daughter, Analise. Unlike her childhood days when physical activity drained her energy and left her ragged and breathless, it's part of her daily routine.
"Running around after a 2-year-old is very demanding," she said. "There isn't much I can't do."
She exercises three times a week, running on the treadmill or weight training. She takes immune-suppressing drugs to prevent organ rejection and abides by doctor's orders.
"I'm strict with myself, because I value what I have," Farley said. "I've been given a gift. It's my responsibility to take care of it."
It stems from the guilt she felt as a child, realizing that her heart came from a boy who died young.
Another patient, Katy Holland of Erie, Pennsylvania, felt similarly after receiving a heart transplant when she was 14.
"I found out my donor was younger," said Holland. "When my mom told me that, I started crying. It made me sad that little kid died, and now I'm alive. He was 9. That's the time that hit me. It's the other person and how sad that someone would die that young."
The donor was 9-year-old Matthew Abraham of Gainesville, Missouri, who had brain injuries after falling from the second floor in his house.
"We've never regretted it for a moment -- not for a moment," said Melinda Abraham, Matthew's mother, about the family's decision to donate his organs.
Holland needed a transplant because she was born with a heart that functioned at half-strength. By the time she was a teenager, she was weakening, and her body was unable to retain protein.
In 2005, Holland received Matthew's heart in an operation at the Cleveland Clinic.
Holland, now a freshman at University of Akron in Ohio, hopes to be a child life specialist and assist other pediatric patients. She lives in the dorms, and follows her daily regimen of immunosuppressants. She tries not to worry.
"The problem is that transplanting is new," she said. "It hasn't been around long enough, and it's always changing so much. I probably need another transplant, no one knows when that is."
About 450 pediatric heart transplants were reported to the International Society for Heart & Lung Transplantation in 2007.
"We don't know what the survival is going to be for someone transplanted in 2000 or beyond," said Boyle, Holland's pediatric cardiologist. "We know they're doing a whole lot better than we had anticipated."
The point is not to live under fear or anxiety, said Farley.
As a child, "I learned that having a transplant would make me better, and my job was to get better," she said. "So that's what I focused on. Of course, there's always fear. If I get sick, if I get the flu, a million things go through my mind. I look at more positive things and how successful I am."