A new heart, a pacemaker and three surgical teams were unable to save Cheyenne Pyle, a baby girl believed to be the nation's youngest heart transplant recipient.

Cheyenne died Thursday at Jackson Children's Hospital, where she was born Nov. 10."She never left the newborn intensive care unit," hospital spokesman Omar Montejo said.

Born with a defective heart, the daughter of Stephen and Alberta Pyle of Fort Lauderdale was given an 80 percent chance of surviving after a five-hour transplant that started when she was just 90 minutes old. Cheyenne's surgery was performed by 35 people in three surgical teams.

But Wednesday she developed a chemical imbalance in her blood, causing her heart to beat too slowly, which in turn lowered her blood pressure, hospital officials said.

Doctors used drugs and a pacemaker to try and control her heartbeat but she did not respond.

Cheyenne had hypoplastic left heart syndrome, a condition that affects about 150,000 children a year. The defect causes an artery to close, cutting the blood supply to the body within a day or so.

The second youngest transplant recipient had surgery beginning at three hours, according to Mark Sampson at the United Network for Organ Sharing, checking records through 1994, the most recent available.