Each year millions of people around the world survive heart attacks but then must live with scarred, weakened hearts that frequently enlarge to compensate for a diminished ability to pump blood. Ultimately, this condition can lead to heart failure and death. Researchers are finding some early signs that replacement cells from an unlikely source-leg muscle-could bulk up diseased hearts, helping to prolong life in heart attack victims.

Genzyme of Cambridge, MA, is now conducting tests of the treatment strategy in France and several other European countries with 300 heart attack patients. Researchers take muscle cells from a patient, cultivate a select group of those cells in petri dishes for two to three weeks, and then inject them directly into the heart’s scar tissue. Preliminary research suggests these replacement cells strengthen the damaged wall of the heart, preventing bulging, says Ralph Kelly, vice president of clinical research for Genzyme.

GenVec of Gaithersburg, MD, and Bioheart of Weston, FL, have begun human tests of a similar technology in the United States. If the trials go well, in five to ten years, leg-muscle-cell injection could become an approved therapy, says John Fakunding, program director for heart research at the National Heart, Lung, and Blood Institute in Bethesda, MD. The treatment could potentially prolong life, Fakunding says. “The transplantation [of muscle cells] into the heart does appear to have a functional benefit,” he says, “in that it may make the heart work better.”

Most experts, however, suggest that the use of leg muscle is a short-term patch. For one thing, leg muscle cells don’t beat, as cardiac cells do. And some researchers suspect that implantation can lead to arrhythmias, or irregular heart beating, in some patients. But leg muscle cells may well play a role “until better reparative methods, using other cells and transplantation methods, are developed,” Fakunding says. Despite the caveats, that’s hopeful news for people at risk for heart failure.