A hospital said Friday it successfully operated on a highly premature newborn for tetralogy of Fallot, a complex heart condition comprising four separate defects.

Okayama University Hospital said it was the first such surgery ever completed successfully in Japan.

Cardiovascular surgeon Shunji Sano, who carried out the procedure, said it could well be the world's first successful case of complex cardiac surgery on an infant weighing less than 1 kg.

The girl, who weighed only 895 grams when she was born on March 15, was diagnosed with tetralogy of Fallot and underwent two bypass surgeries using artificial blood vessels to direct blood from the subclavian artery to the pulmonary artery.

Sano, who specializes in pediatric congenital heart diseases, said the girl underwent two operations — in April and September — and is expected to be released soon.

Tetralogy of Fallot, often diagnosed at birth or soon after, causes the heart to pump oxygen-poor blood around the body. Infants and children with tetralogy of Fallot tend to have blueish skin because of lack of oxygen.

"I'm so happy my daughter's condition has improved enough to let us see her smile," said the girl's 30-year-old mother. "I'm looking forward to the day we will be able to take her outside."

At a news conference on Friday, Sano said the girl's case has proven that the surgery can be performed on even very small infants.

"We want other people not to give up hope," he said.