The peer-reviewed trial involved giving the babies paracetamol.

The heart problem, patent ductus arteriosus (PDA), is a medical condition in which extra blood flows to the baby's lungs at birth, making it difficult to breathe.

It affects half of those infants born at less than 29 weeks.

The trial involved 58 babies aged between 23 and 28 weeks being given paracetamol for five days every six hours from the day they were born.

The results show early treatment with paracetamol reduces the need for intervention to close the fetal blood vessel in the premature babies, with no known side effects.

The trial was led by neonatologist Tim Schindler at The Royal Hospital for Women in Randwick and it involved dozens of doctors and nurses. It was carried out over a two-and-a-half year period from November 2016 to March 2019.

Dr Schindler told AAP the results were "practice-changing".

"If we have a safer alternative then clinicians are more likely to choose paracetamol than the traditional medications that we've used in the past," he said.

Dr Schindler believes the results will have far-reaching consequences.

"It's been quite an exciting result, because the medications that we traditionally have been using are associated with some side effects, some of which are quite serious and paracetamol is potentially safer for these vulnerable babies.

"The medications we have been using have side effects risking damage to other organs in the body, in particular the kidneys and the gastrointestinal system, even perforating the bowel.

"We didn't observe any side affects in paracetamol, however larger studies are needed," Dr Schindler said.

The trial outcomes have been published in the Neonatology Journal.

Australian Associated Press