Non-human primates would be the ideal, because they are genetically closer to humans, lessening rejection risks. Though it may seem logical to use organs of non-human primates, these animals are not ideal sources for xenotransplantation. Because monkeys and apes have long gestation periods and few offspring, they would not supply enough organs to significantly reduce the shortage of organs. Finally, since baboons are our cousin-like species, this raises the risk of transmitting human pathogens. Using baboons would cause a lot of concern since they are our cousin-like species.
Pigs have heart that are strikingly similar to that of humans.
And they are generally healthier than most primates and they are extremely easy to breed, producing a whole litter of piglets at a time. The life-cycle of the pig is short enough so that it can be raised in captivity and we would not have to wait twenty years for a mature pig heart. Moral objections to killing pigs are fewer, since they are slaughtered for food. More than ninety million pigs are slaughtered each year in the United States for food. Many of their heart valves are regularly used to replace diseased or damaged heart valves.