A South Carolina teenager said she felt like a "fake person" living for 118 days without a heart beating in her chest in-between heart transplants.

D'Zhana Simmons, 14, was released Wednesday from a Miami hospital after being kept alive on a custom-built artificial blood-pumping device.

"You never knew when it would malfunction," Simmons said, her voice barely above a whisper, at a news conference at the University of Miami/Jackson Memorial Medical Center.

"It was like I was a fake person, like I didn't really exist. I was just here," she said, referring to the time without a heart.

D'Zhana had dilated cardiomyopathy, which caused her original heart to become enlarged and too weak to pump blood sufficiently.

When her first transplanted heart also did not work properly in July, surgeons replaced it with two heart pumps until she recovered her strength.

Medical feat 'pretty amazing'

Normally when an artificial heart is used as a bridge, the patient's own heart is left in the body, doctors said.

"This, we believe, is the first pediatric patient who has received such a device in this configuration without the heart, and possibly one of the youngest that has … been bridged to transplantation without her native heart," said Dr. Marco Ricci, the hospital's director of pediatric cardiac surgery.

It was a "big deal" for a child to be left without a heart for so long, said Dr. Peter Wearden, a cardiothoracic surgeon at Children's Hospital of Pittsburgh.

"For (more than) 100 days, there was no heart in this girl's body? That is pretty amazing," said Wearden, who works with the kind of pumps used on the teen.

An adult in Germany had been kept alive for nine months without a heart, the Miami team said.

D'Zhana overcame kidney and liver failure and gastrointestinal bleeding. She had a kidney transplant the day after her second heart transplant.

It took the help of four people to help her take a short stroll, including one person who steered the photocopier-sized pumping device.

Her prognosis is good, Ricci said, but there is 50 per cent chance that she will need another heart transplant before she turns 30.

For now, D'Zhana said she is glad she can now walk without the machine. She is looking forward to celebrating her 15th birthday on Saturday riding a boat off Miami's coast, and is grateful she will be able to see her five siblings and friends again soon at her home in Clinton, S.C.