The technique, in which tissue is cut out of the heart, is called "left- ventricular reduction" and overturns the canon of cardiac surgery that healthy muscle should not be removed.
Professor Gianni Angelini, the British Heart Foundation Professor of Cardiac Surgery at Bristol University, has performed five of the operations on patients who were terminally ill. The procedures were the first to be carried out in Britain.
Conventional surgery, including heart transplants, was not an option for the patients at the Bristol Royal Infirmary, who were hardly able to walk and had extreme breathing difficulties. Three of the patients survived the operation and were able to go home in considerably improved health, although one died months later due to causes unrelated to the surgery.
Of the two patients who did not survive, one died of kidney failure and another from a surgical complication.
One of the survivors is Garry Payne, 50, an estate agent, of Lichfield in Staffordshire. After suffering three heart attacks in 1994, Mr Payne was given six to twelve months to live. His GP referred him to Professor Angelini, who convinced him to opt for the experimental technique. "I was under no illusion at all about what he was going to do. He was most emphatic that it was high risk and extremely adventurous surgery," Mr Payne said.
The operation has largely freed him from severe angina, extreme breathlessness and tiredness. "I am still being treated for some residual pain and cannot work because of stress. But I believe I have a better future now.
"Downsizing the heart is not a miracle cure, but there is no doubt it does improve quality of life."
It takes around two hours from the first stroke of the surgeon's scalpel to the sealing of the wound. A heart-lung machine is used while the heart is exposed. The surgeon cuts into the left ventricle, the main muscular chamber of the heart which accounts for two-thirds of the heart's volume.
Disease can stretch the walls of the ventricle, increasing its overall volume and making the heart work harder. The surgeon removes a piece of the ventricle, then stitches and reinforces the cut, reducing the volume of the ventricle by 30 to 40 per cent. In most cases, the mitral valve is replaced by a mechanical alternative.
The new operation has advantages over heart transplants in that it is cheaper, quicker and requires less after-care. There are only 400 heart transplant operations in Britain each year, although there are thousands of patients on the waiting list. Professor Angelini hopes that the new technique could offer an alternative.
He said: "It is high-risk pioneering surgery and we are in largely uncharted waters. However, it has enormous potential for greater numbers of patients than heart transplants."
The groundbreaking surgical work features in the BBC1 QED programme on Wednesday.