A third patient implanted with an artificial heart made by French firm Carmat is doing well six months after his operation, the company's CEO said on Wednesday.

The 73-year-old patient was operated on April 8 and went home from the hospital in August. The first two patients to receive Carmat artificial hearts have died - the first 74 days after being operated and the second after nine months.

"The third patient is doing well. He lives alone near Strasbourg and goes to the hospital once a week for checks. He has a good quality of life," Carmat Chief Executive Marcello Conviti told Reuters on the sidelines of a conference in Paris.

He declined to comment on remarks in June by the professor who invented Carmat's artificial hearts that a fourth patient would be fitted with an implant in the coming months.

Carmat is conducting trials of its heart device that is designed as a permanent implant to extend the life of patients without them having to wait for a human heart donor.

After four patients have received the heart and survived for at least 30 days, the trials are to be enlarged to about 20 patients at the European level.

"Today we've had patients exposed to the machine for (a total) of 18 months," Conviti said. "For now everything is going well."

Carmat's first transplant patient, a 76-year-old man, died in March last year, two-and-a-half months after his operation.

The second patient died in May after the artificial heart malfunctioned due to a fault with one of the controls in its motor, but no fundamental problems were found with the device