Baby Fae was the first successful infant heart transplant, receiving the heart of which animal?

Stephanie Fae Beauclair (October 14, 1984 – November 15, 1984), better known as Baby Fae, was an American infant born in 1984 with hypoplastic left heart syndrome. She became the first infant subject of a xenotransplant procedure and first successful infant heart transplant, receiving the heart of a baboon. Though she died within a month of the procedure, she lived weeks longer than any previous recipient of a non-human heart. A baboon heart was used as there was no time for a suitable human heart to be found.

The procedure, performed by Leonard L. Bailey at Loma Linda University Medical Center, was successful, but Fae died 21 days later of heart failure due to rejection of the transplant. The rejection is thought to have been caused largely by a humoral response against the graft, due to Fae's type O blood creating antibodies against the type AB xenograft. The blood type incompatibility was seen as unavoidable: fewer than 1% of baboons are type O, and Loma Linda only had seven young female baboons (all of which were type AB) available as potential donors.