Michelle Johnson, 38, is only the 24th person in the world to receive a battery-powered artificial heart.Johnson depends on the device that, from the outside, looks similar to a backpack. But it's what is inside the backpack that allows the mother of three to continue living."It's kind of hard to believe I'm living off a machine, but I'm still here," Johnson said.Johnson was diagnosed with congenital heart failure and her body recently rejected a previous heart transplant. Her only hope was an artificial heart, so doctors implanted the SynCardia Heart Pump. The tubes connect her body to the backpack, allowing blood to flow."Now patients can go home with a 13-pound device either on their back or as a carry-on," said Dr. Jaime Moriguchi of Cedars-Sinai Medical Center in Los Angeles.Johnson was the first heart patient at Cedars-Sinai Medical Center in Los Angeles to undergo the procedure. She said she most looks forward to being with her three children, and said her youngest son cannot wait for his mother to come home.Her family is taking care of her during her recovery and rehabilitation. Both her mother and brother, Mark, are trained on how to operate the device if the artificial heart malfunctions.Unfortunately, Johnson cannot live on the artificial heart, and she will need a heart transplant later on. However, she said she is optimistic a future procedure would be successful."It's just great to have another chance at life," she said.The operation was done in partnership with UC San Diego's Sulpizio Cardiovascular Center.