Various types of cell transplant have been tried—albeit with limited success—to repair the damage to the heart inflicted by a heart attack. However, two studies raise hopes that cells from a patient's bone marrow could be used to rescue injured hearts. In one study, researchers at Columbia University (New York) extracted a specific subpopulation of stem cells from human bone marrow—so-called angioblasts—that give rise to the endothelial cells lining blood vessels. When injected into the tails of immune-deficient rats, the angioblasts migrated to the heart, triggering the growth of new blood vessels in both damaged and undamaged myocardium (Nat. Med. 7, 430–436, 2001). There was a 30%–40% inprovement in heart function in rats treated with stem cells. A different tactic was employed in the second study, in which a specific population of multipotent cells was injected directly into ischemic mouse heart (Nature, 410, 701–706, 2001). The cells, which were tracked using a green fluorescent protein label, took up residence in the damaged tissue and created not only new blood vessels but also new cardiac muscle. Moreover, there was a measured improvement in heart function in transplant recipients. Although there are many questions still to answer about the viability of this approach—the least being the practicalities of harvesting stem cells from heart attack patients—the researchers say there is “compelling evidence” that the technique could benefit humans.