I wasn't born with a heart problem; I was a normal, healthy baby until I got a chesty cough and runny nose at the age of five months, in August 1987. Everyone thought it was just a cold until suddenly I had difficulty breathing and my lips turned blue. I was rushed into hospital where an x-ray showed that I had contracted dilated cardiomyopathy, a condition that destroys the heart muscles. My parents were told that unless I had a heart transplant I would die.

The operation had been performed only twice before on babies in the UK and neither attempt had been successful. At first, the Freeman hospital in Newcastle advised my parents to take me to the United States where they had more experience of heart transplants. However, I became too ill to make the journey so the hospital offered to carry out the operation. Six weeks later a donor heart became available. The operation took six-and-a-half hours and mum says it was the longest day of her life. I don't think anyone thought I had much of a chance but it went well and I was home by Christmas.

My new heart was the size of a walnut and in those days, no one knew if it would grow with the rest of me or not. Every day, my family were amazed I was still alive. My parents were told I'd probably need another transplant after about two years but that date passed without incident, and then we were told I might be OK for another five years. Soon 10 years had gone by and now, at 21, I've stopped counting. I'm very lucky - my life would have been very different if I'd had to have major surgery throughout my childhood.

I didn't fully understand about my transplant until I was eight years old. As far as I was concerned, I was exactly the same as other children. I wasn't late learning to walk or talk and I just assumed that, like me, everyone had to take medication (immunosuppressant drugs to prevent my body rejecting the heart). From early on, my mother had explained that when I was a baby my heart hadn't worked and I'd been given a new one, but it didn't really sink in.

Then, one day, I asked her about the scar down my chest and she told me that when I needed the transplant, a baby had died in a car accident and the baby's family kindly allowed me to have her heart. It took me a long time to get my head around it. Until then I'd honestly thought that the hospital killed babies and kept all the different organs hidden away in cupboards until they were needed for transplants.

I still don't know the details of the operation and I prefer to keep it that way. It's not just that I'm a bit squeamish about it; I don't think I've really come to terms with it, emotionally. My donor's father lives locally and I've been told through friends that he sees me about occasionally. I do worry about how he feels when he sees me. It must make him think about his baby; she was only a few months older than me so we might have been at school together. I don't want to meet him at the moment - I think it would put too much pressure on us both - but he knows I'm very grateful and I have huge respect for him.

I had a normal upbringing. If my parents felt over-protective towards me, they were careful not to let it show. I wasn't able to take part in contact sports or anything that might injure my abdomen, but I could join in with everything else. I hated PE at school but I've been competing in the Transplant Games since I was two, when I won a gold medal for wellie-throwing. This August I'm going to Australia to represent the UK in the 100m, 200m, relay race and tenpin bowling at the World Transplant Games. I'm also training with the Gateshead Harriers, a local running club.

What I like most about the Transplant Games is mixing with other transplant recipients. I have some lovely friends who haven't had transplants but I always feel I have to be careful about what I say because some people have very strong feelings against organ donation, which obviously I find quite upsetting. I used to get a bit of name-calling at school too; kids would ask me if I had a pig's heart and if all the drugs I took were legal. And, more recently, someone came up to me at work and said, "I'm surprised you're still here."

I haven't had any major health problems. Once, when I was at primary school, I got chest pains and was taken to hospital by air ambulance, which was frightening, but it turned out I'd just got a bad chest infection and needed antibiotics. However, if I catch a cold or the flu, I have to go into hospital because the drugs weaken my immune system. I might have to have a lung transplant in the future.

But I have a fantastic life. I have a big circle of friends and I go to parties and have a drink like anyone else my age, although I'm careful not to overdo it. I work at Marks & Spencer as a sales adviser and I'm hoping to be a visual merchandiser. Everyone says I'm going to get married to someone who's had a transplant, and I did have a boyfriend for a while who had also had a heart transplant, but it's a big world out there, so we'll see.

Every year, my family and I celebrate my transplant anniversary and we always remember the donor family, because without them I wouldn't be here.

• Kaylee Davidson was talking to Hilary Whitney

UK transplants: facts and figures

• Kaylee Davidson is the longest-surviving person in the UK to have had a heart transplant as a baby. Two years ago, Sarah Cox became the youngest baby to survive the operation, at just 23 days old.

• According to the latest UK figures 7,875 people, including 154 children, are waiting for an organ transplant: 94 need a heart 13 need both a heart and a lung while 6,938 need a kidney.

• Statistically, you are more likely to need a transplant than you are to become a donor.

• Organ donors have traditionally come from two groups: road accident and brain haemorrhage patients. Improved road safety and medical treatment mean that fewer in both groups are dying.

• The number of people needing a transplant is expected to rise steeply in the UK over the next decade due to an ageing population, an increase in kidney failure and scientific advances resulting in more people being suitable for a transplant.

Organ Donor Line: 0845 60 60 400 or uktransplant.org.uk