A two-month-old Spanish girl's life was saved thanks to groundbreaking surgery in which doctors transplanted a small heart from a donor of a different blood group into a small heart that had stopped beating.

On Monday, Juan Miguel Gil Jaurena, head of children's cardiac surgery at the Hospital Gregorio Maranon in Madrid, said, "It was twice the magic."

He clarified that three years ago, such techniques did not exist for young children and had never been used on a baby so small.

The case paves the way for more babies who need heart transplants but are too young to rely on ventricular assist devices before a suitable donor becomes available.

The operation was complicated by the fact that the donor was in a hospital in another part of Spain, and the heart had stopped beating for a few minutes, necessitating a rehabilitation procedure. The donor's identity was kept a secret by the hospital.

Naiara, the baby girl, had been diagnosed with congenital heart failure before she was born and weighed just 3.2 kilograms at the time of surgery.

"She is the tiniest baby we've ever had for a heart transplant, and her health had deteriorated dramatically just 24 hours before the surgery. She would not be alive today if she hadn't received a heart transplant "Manuela Camino, the director of the children's cardiac transplant unit, explained the situation.

Naiara is doing well in the hospital.

According to the World Health Organization's (WHO) global database on donation and transplantation, which is managed by the Spanish Transplant Organization, Spain was the world leader in transplants last year with 37.4 donors per million people (ONT).