A brave Brazilian man is fighting for his life — with two beating hearts inside his body.

The unnamed 53-year-old is in a stable condition after a 12-hour operation.

But doctors at Sao Paulo's Heart Institute fear he only has a 50 percent chance of surviving.

The patient has suffered severe lung hypertension that stopped his heart pumping blood around his body.

So he was given the new donor organ to prop up his own heart.

The "new" heart was placed on the right side of his chest and is linked to his original heart by a vein, arteries of the lung and the aorta.

"This is not a routine transplant, the situation is exceptional," Surgeon Alfredo Fiorelli, who carried out the transplant, said. "The next 72 hours will be fundamental to evaluate his state."

"One heart would not be capable of pumping enough blood to the whole body since the patient's lungs were damaged.

"The traditional transplant would not be recommended and the only alternative was placing a second heart besides the original one as an aide."

He added: "The patient will be kept alive in an artificial state for two months. Without this operation, the patient's chances of survival were unlikely.

Click here to read more on this story from The Sun.