Parents have called on support for their campaign to keep the children's heart surgery unit at Oxford's John Radcliffe (JR) hospital.
The centre is one of 11 paediatric heart units being assessed for their viability, in a national review.
The results of the study are expected to be published later this year.
More than 1,000 people have joined a Facebook group calling for the Oxford unit to be saved and some members were due to meet in the city on Tuesday.
Maria Crocker, from Berinsfield, started the group in April, as her eight-year-old son David has a heart condition which might require surgery.
She said David would prefer any operation to take place in Oxford rather than at other centres in Birmingham or London.
"He is very adamant that they shouldn't withdraw Oxford from performing surgeries. He now likes going to Oxford as it is familiar to him."
Mrs Crocker believes the JR could become a diagnostic centre and called on support from people in Oxfordshire.
She said: "The other units around the country all see it as a threat, even the ones that have got bigger units than us.
"So Oxford needs to be prepared and needs to fight for it as well."
The NHS National Specialised Commissioning Group will recommend which centres should stop doing surgery, and which should be expanded.
The JR's chief executive Sir Jonathan Michael said the Oxford unit had a lot to offer, despite being the smallest of the centres being assessed.
"It is felt that we have a number of definite strengths in terms of geographical location and the co-location of services that not all other centres can provide."