A man who has had six heart attacks is one of the first UK patients to undergo an experimental cell transfer.
Mr Jackson has already had a heart bypass operation
Doctors have injected immature muscle cells from his leg into scarred heart tissue in a bid to repair the damage.
Ron Jackson, 59, from Rutland, had the operation at Leicester's Glenfield Hospital. He will have to wait months to see if the treatment is successful.
The main risk is that the leg muscle tissue could alter the heart's rhythm, heart specialist Tony Gershlick said.
The special cells from the muscle were sent to a lab in Belgium where they were cultured.
Two weeks later they were sent back to Leicester to be used in a second operation.
Consultant cardiologist Tony Gershlick said: "We haven't taken the muscle cells from the leg but the immature cells from the outside of the muscle bundle.
"They are ones that undertake repair (if you suffer a muscle injury)."
Four other patients are expected to undergo the procedure at Glenfield Hospital along with several others at London St Mary's.
The research team in Leicester said one advantage of this procedure was that the cells were from the patient's own leg.
Other research projects involve using stem cells which can pose ethical questions about their origin.
The cell transfer research is also being done in other European countries including Poland, Holland, Spain, Belgium and Germany as part of an international trial.
The patient's heart is still beating during the operation as the cells are injected into the damaged area. Ultrasound and X-ray are used to guide a fine tube to the damaged heart muscle.
Dr Gershlick said the breathlessness experienced by heart attack patients can be treated by drugs and pacemakers but in some cases this is not enough to solve the problem.
"For some time there has been a concept that if we could take immature cells and put them in the scarred area they might start to perform and function as heart muscle cells," he said.
"We hope these cells - which won't necessarily grow into heart muscle tissue - will act as if they are heart muscle tissue."
Mr Jackson said: "A heart attack can damage the muscle, so if this is going to make it grow back then that is great news."
His wife Margaret said: "It is something a lot of people couldn't do but Ron seems to have something within him."