Morgan Porter's new heart began beating in the pre-dawn darkness Wednesday.

The 3-year-old girl received the organ in surgery at the Medical University of South Carolina. It was donated by the family of a child with a head injury.

"Luckily, this heart is a very good match. She's doing well," said Dr. Minoo Kavarana, the transplant surgeon.

Morgan had been kept alive since last summer by a mechanical pump known as a "Berlin Heart." It's a ventricular assist device that uses external pumps to take blood directly from the atria and pump it to the lungs and the body, thereby taking the load off the heart's ventricles. Removing the device was more difficult than usual because much scar tissue had formed around it during the six months it was in place, he said.

"She had a very long operation," Kavarana said.

The surgery began about 10:30 p.m. Tuesday and lasted some six hours. With the new heart in place and pumping, doctors worked for another two hours to control bleeding. The first 24 hours after surgery are key, he said.

"We wait and watch very closely," he said.

In a week or so, Morgan should be able to get out of bed, he said.

Heart transplants for children as young as Morgan are relatively rare. From 1988 through last October, 457 heart transplants have been performed at the Medical University. Only 27 of them were on children younger than 5, according to the federal Organ Procurement and Transplant Network.

After being removed from the donor body, the heart Morgan received was on ice for about four hours. When it was placed in her chest, a clamp was loosened and blood flowed into it. In response, the heart came alive and began doing its job of circulating blood throughout her body, he said.

Details about the donor are private under law, he said.

The heart she received is "very good quality," he said.

The transplant process began Tuesday afternoon. While Morgan was being prepared for surgery, a team from the Medical University traveled to an undisclosed location to remove the donor heart. Timing is critical because a heart out of the body more than six hours is at risk of failing, Kavarana said.

The new heart for Morgan was flown here. It arrived in a box, just like her mother Sarah Porter had told her would happen when God sent it. The donor and recipient teams stayed in constant contact so their actions would be highly synchronized. When the new heart arrived, Morgan was ready to receive it.

Doctors will close her chest cavity after about 48 hours as her recovery progresses in the pediatric intensive care unit for heart patients.

"The important thing now is keeping her germ-free," said Heather Woolwine, Medical University public relations director.

Morgan's father is Marine Corps Maj. Robert Porter. He is a fighter pilot who served in Operation Enduring Freedom and Operation New Dawn. The girl fell ill with flu-like symptoms in July after a weekend trip the family made to Charleston from their Lady's Island home. Doctors here said her heart was not pumping properly, and it was a life-threatening situation. She needed a transplant.