Heart transplantation is a proven treatment option for Class IV heart failure patients, but a limited number of donor hearts become available each year.

FORBES: HeartWare Beating Away, Pulse Still Strong

They give the heart muscle time to rest or recover and can support the failing heart until a donor heart becomes available for transplantation.

BBC: Image of heart failure

However, no rabies test was done before the before the donor's kidneys, heart and liver were delivered for transplantation in September 2011, the CDC said.

CNN: CDC: Man died of rabies from kidney transplant

At the time, rabies wasn't suspected as the cause of the donor's death, and no rabies test was done before the donor's kidneys, heart and liver were delivered for transplantation in September 2011, the CDC said.

CNN: CDC: Man died of rabies from kidney transplant