The frontiers of organ transplantation have been pushed further than ever before. The first organs taken from genetically engineered pigs have been put into people and the recipient of the first pig heart managed to survive for two months. If the body unleashed a horrendous assault on the foreign organ – holes would be ripped in every cell in the pig tissue and the organ would clot from the inside out.  Thereafter it would have gone splotchy, then blue, then completely black within minutes.  If “hyperacute rejection” is avoided, the organ would blush pink with the flow of blood and oxygen. The latter happened during this transplant and this operation was just one of a series of medical breakthroughs that have renewed interest in the field of xenotransplantation.
Source: BBC