Several children's heart surgery units across England should be closed with operations done by fewer, specialised centres, according to an expert review.
It was launched after the 1990s Bristol heart babies scandal when children having heart surgery died needlessly.
The BBC has learned that all 11 paediatric heart centres are being assessed to decide which to keep open.
The intention is to improve care, but patients' groups say long journeys could put pressure on families.
There are currently 31 surgeons in 11 centres across England carrying out heart operations on children.
Their work first came under the spotlight after it emerged that children had died unnecessarily following heart surgery at the Bristol Royal Infirmary between 1991 and 1995.
Experts have already advised that fewer, larger centres of excellence would provide better care for children needing heart surgery.
The NHS National Specialised Commissioning Group is now assessing which centres should stop doing surgery, and which should be expanded to provide the best, most specialised care.
A report by the group says a balance has to be struck between services that are close to home and services that provide enough specialist skills to provide the highest standards of care.
At the moment, four children's heart surgery centres have only one or two paediatric surgeons. The report says this means there are times when a surgeon is not available to deal with routine cases or emergencies, and that they may have more limited expertise.
There are no plans to cut the overall number of surgeons, but it is likely some would have to move to different centres.
Each would have a minimum of four surgeons. The centres that stopped doing surgery could continue doing non-surgical treatments like diagnostics out-patient care.
NHS medical director Sir Bruce Keogh said the proposals put the interests of children first.
"If we don't address this issue we will put some of the most critically ill children at risk and fail in our duty to ensure these NHS services are fit for the future," he said.
The Patients Association said it was not opposed to reorganisations of specialist services when there were good clinical reasons, but it said if surgical units were closed, patients and their families could face long journeys for treatment.
"Some people have friends and family they can call on for support, but not everybody does," said spokeswoman Katherine Murphy.
"If the NHS is to be a truly comprehensive health service it needs to be mindful of these needs and help families and carers cope with the very real difficulties that can be created."