Its longevity is a milestone. Previously, when researchers tried to transplant pig hearts into primates, the primates' bodies would reject the transplants within six months, The Telegraph reports. Ultimately, researchers want to make pig hearts transplantable into humans. Pigs could provide a larger supply of the organ than human donors can, closing the tragic gap between supply and demand. In the U.S., about 3,000 people are on the waiting list for a heart transplant, but only about 2,000 hearts become available each year, according to the U.S. National Heart, Lung and Blood Institute, which conducted the baboon study. Those who are waiting can use mechanical devices, but those aren't perfect, the institute says.