Mitochondria are tiny organelles that fuel the operation of the cell. A series of experiments has found that fresh mitochondria can revive flagging cells and enable them to quickly recover. In animal studies ... mitochondrial transplants revived heart muscle that was stunned from a heart attack. Infusions of mitochondria also prolonged the time organs could be stored before they were used for transplants, and even ameliorated brain damage that occurred soon after a stroke. In ... human tests, mitochondrial transplants appear to revive and restore heart muscle in infants that was injured in operations to repair congenital heart defects. The idea for mitochondrial transplants was born of serendipity. Dr. Emani is a pediatric surgeon. Dr. McCully is a scientist who studies adult hearts. Both were wrestling with ... how to fix hearts that had been deprived of oxygen during surgery or a heart attack. One day, [Dr. McCully] decided simply to pull some mitochondria from healthy [pig] cells and inject them into the injured cells. To his surprise, the mitochondria moved like magnets to the proper places in the cells and began supplying energy. The pig hearts recovered. Meanwhile, Dr. Emani was struggling with the same heart injuries in his work with babies. [When] the two researchers met, it was almost an 'aha' moment," Dr. Emani said. The scientists have now treated 11 babies with mitochondria. All of the more recent patients survived and are doing well.