Heart attacks killed 267 out of 100,000 people in 2007.
If everyone who had a heart attack or fatal heart disease was saved then 700,000 people in the USA and 7.1 million people worldwide would be saved each year.
During a heart attack, the heart muscle dies within days and the scar doesn't contract, Okarma said. So, over time, the heart enlarges, increasing the diameter of its chambers.
However, in the study, cardiac cells injected into the ventricular wall of the heart decreased the diameter of the left ventricle, rebuilt the heart muscle wall and improved the strength of the contracting heart muscles, according to Okarma.
"The animals that got our cells, four days after the infarction [heart attack], didn't enlarge — the heart stayed small because the heart muscle cells we put in are functional. They prevented the onset of heart failure.
"Our cardiomyocytes are the first human cardiac cells shown to survive after injection into an infarcted ventricle and to produce significant improvement in heart function," Okarma said.
Four weeks after the transplant, the hearts of the rats that received the cardiac cells were scanned with an MRI to assess the growth of new tissue and to determine whether the injected stem cells had migrated to other organs.
The scientists discovered that the newly introduced cells remained solely in the heart and that no tumours or cysts developed — a common occurrence when foreign cells are transplanted into the heart.
Okarma said studies on sheep are currently underway. He predicts human trials will occur in two to three years.
"This will become the treatment of choice for patients who suffer a heart attack," Okarma predicted, "because no pill fixes a broken heart."
Sifting through a slew of biochemical factors that were known to be involved in heart formation, researchers came up with a formula that greatly increased the yield of heart tissue from the stem cells.
"Typically one tenth of 1 per cent of the (stem) cells would make heart muscle, maybe 1 per cent on a really good day," Murry says. "Now we're getting 38 to 50 per cent of the cells turning into heart muscle."
In total, the combined procedures increased the proportion of successful cell grafts from 15 per cent to 100 per cent in the rodents, who went through lab-induced heart attacks.
The size of those grafts went from "tiny clusters of cells" under the old methods to upwards of 10 per cent of the damaged heart region under the new.
Murry hopes to bring the research into clinical human trials within three years, but will test it on pigs or other large mammals first.
He says it may have applications for stem cell therapies on other organs that have similar production and transplantation hurdles.
"The problem with cell death in cell transplantation (for example) is something that has plagued repair of all solid tissues so far," Murry says. "It's our hope that this will be useful outside of the heart as well."