With the increasing availability of pigs genetically engineered to protect their tissues from the human immune response, research into xenotransplantation is progressing steadily. One potential route to the clinic would be the use of a pig heart as a bridge to allotransplantation. This would only be ethical if the outcome was realistically estimated to be as good as, or better than, bridging with a mechanical device. The experimental results that would be required to warrant consideration of a clinical trial and the patients in whom bridging with a xenograft might be considered preferable to a mechanical device are discussed. © 2010 International Society for Heart and Lung Transplantation. All rights reserved.