Tom Christerson received the completely implantable AbioCor artificial heart Sept. 13 -- the second subject to receive the device. Robert Tools, who received an artificial heart in July, died Nov. 30, after surviving 151 days.

"Tom is making steady progress," said Dr. Rob Dowling. "Each day, I see some improvement in his condition."

Christerson was moved to the hospital's telemetry monitoring unit for cardiac patients.

Christerson's other doctor, Laman Gray, said though the patient is still extremely weak, he usually takes a few steps every day with the help of a walker and has taken short trips around the medical campus. On Wednesday, he took a ride through downtown Louisville, accompanied by his wife.

The doctors said Christerson, who suffers from chronic obstructive pulmonary disease, is breathing without a ventilator and he's stopped running fevers, but he's still having trouble swallowing.

Six subjects so far have participated in the AbioCor trials. One died on the operating table. Patients selected for the trials were among the sickest, given no more than 30 days to live.