Triathlete with her heart set on glory On Sunday, Corinne Ellison will compete in one of the world's toughest sports events in order to fulfil the promise she made to herself two years ago while lying, terrified, on a hospital trolley waiting to have major cardiac surgery. The 29-year-old will compete in the Austrian Ironman Triathlon in which she'll swim for two and a half miles and cycle for 112 miles, before running a marathon. "I just can't wait," she said. I've come so far, I want to complete this triathlon now. Ellison, from Bournemouth, had just started running marathons as a way to keep fit when she first suspected there was something wrong with her heart. I reached a point, at the end of 2009, when I started feeling really exhausted. I put it down to doing too much, but I'm a nurse and there was a part of me that knew something more serious was wrong. The symptoms got worse. Ellison found herself feeling breathless and suffering from frequent palpitations and chest pains. A test called a transesophageal echocardiography, which uses soundwaves to create detailed images of the heart, revealed that she had an atrial septal defect - a hole in her heart. I felt almost frozen with panic. It's hard to describe the shock, and it was really scary when I was told the hole had been there since birth. Apparently, the fact that I'd decided to take up running had exacerbated the symptoms, but it had also been a lifesaver because if I'd just carried on as normal and hadn't discovered the hole in my heart, I wouldn't have made 40. I'm so grateful to sport for showing me that something was wrong. In this type of defect, the wall that separates the upper heart chambers does not close completely, as it normally should after birth. It means the blood flows in the wrong direction, from the left to right chambers. Left untreated, it can lead to pressure in the lungs and heart failure. Dr Robert Henderson, a cardiac consultant from Nottingham University Hospital, says it is estimated that around one person in every 1,000 has atrial septal defect (ASD), but most of those are diagnosed in infancy. Many people are treated for the condition without major surgery, by the insertion of a catheter through a large vein in the patient's inner thigh. The catheter is then advanced into the heart from where a device can be placed on the organ to cover the hole. But Ellison's defect was too large, so open heart surgery was required. In June 2010, she went into Southampton General Hospital for surgery. "They actually stopped my heart for 40 minutes and put me on a bypass machine during the operation," she explains. They broke my sternum, then repaired the hole, using tissue from my heart. The doctor told me that the hole was very big and the blood flow had reversed as a result. She was in intensive care after the operation, but within eight weeks her heart rate had settled and she was able to run on a treadmill. At 12 weeks, her sternum started to heal and she started cycling and swimming. Her dreams of competing in the Ironman began to take shape. "It took six months to get back to normal," she said. I said at the time of surgery that I would do this race. Now I train all the time - I wear compression shorts packed with ice under my nurse's uniform to help my muscles cool down - but it will all be worth it on Sunday. I want to do this triathlon to prove I can do it, and I want to raise awareness about heart defects and show people that it's not the end. In some ways, it can be a whole new beginning.