Sarah Crawford, from Uddingston, South Lanarkshire, was warned that the growth in her heart wall could prove fatal if she did not have it removed without delay.
The 30-year-old had no idea there was anything wrong until she started experiencing dizzy spells, chest pains and breathlessness.
After a visit to her GP in April last year, Ms Crawford, a solicitor, was referred to specialists at Clydebank's Golden Jubilee Hospital who diagnosed the extremely rare condition myocardial fibroma.
There are thought to be less than 150 reported cases in the world and consultants had to take advice from a clinic in the US before deciding to carry out a risky procedure to remove the benign tumour.
Kenneth MacArthur, a consultant cardiothoracic surgeon at the Golden Jubilee, said: "Sarah was already suffering symptoms as a result of this extremely rare condition, to the extent that she was almost experiencing heart failure due to obstruction to the left ventricle.
"In 20 years performing cardiac surgery, I have never seen a tumour as large as Sarah's in a case like this.
"Due to its size and position, surgery was a very risky option as there was a very real chance of causing damage to the surrounding heart, which would have made it impossible to bring her off of the artificial heart and lung machine. In years gone by, this operation would not even have been attempted.
"However, due to the specialised expertise available to us at the Golden Jubilee and the advances which have been made in ventricular assist devices (mechanical hearts) and transplant procedures, it was decided that we were willing to attempt to remove the fibroma."
Ms Crawford underwent open heart surgery on July 22 last year and five days in intensive care followed. She is still attending cardiac rehabilitation sessions which see her take gentle exercise with other heart patients.
On Tuesday, the lawyer celebrated her 30th birthday with family and friends and is looking forward to returning to her job in Glasgow later this year.
She said: "I had no idea there was anything wrong with me, the symptoms came on very suddenly. When I got the tests I thought 'Is this really happening'?
"It was all very scary. My family and I were relieved that the tumour wasn't malignant but there was still fear and shock when we were told about it.
"I sat down with them and we talked about the surgery. My father is a doctor and, although this wasn't something he had ever encountered, it was useful to have his input with the decision.
"In the end I felt it was the only decision that I could make. I knew I had to go ahead with it, even though it was really scary.
"The care I received was outstanding, and the staff at the Golden Jubilee have been fantastic from the moment I stepped through the door. I am so grateful for the skill and expertise of the doctors and staff at the hospital."
Ms Crawford's parents, Rudy and Jean, raised £2,000 for the hospital after asking for cash donations instead of gifts for their ruby wedding anniversary.