D'Zhana Simmons, a 14 year old girl from South Carolina, lived for nearly 4 months without a heart. She suffered from a condition called dilated cardiomyopathy (where the heart becomes weakened and enlarged and fails to pump blood
efficiently) and was waiting for a transplant.
Simmon's blood was kept ciculating by two blood pumps, she said that the experience was "scary" because of the everpresent worry that the machine would malfunction.
"You never knew when it would malfunction," she said 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.
"But I know that I really was here, and I did live without a heart."

Simmons was recently released from the hospital after successfully undergoing her second heart transplant.
(source)