Anne Keatley-Clarke, chief executive of the Children's Heart Federation, has said that families affected by the suspension of the children's heart unit at Leeds General Infirmary are "very worried".
A lot of families have not yet been contacted and there are a lot families that are very worried there about what is going to happen with their children.
We are certainly receiving calls from parents, where they are extremely worried, and indeed at the moment extremely frightened by speaking out.
They are frightened of what might happen, there have certainly been all sorts of threats and we have been advising some of those parents to share the threats with the police, that's up to them if they want to take that forward.
More top news
Detectives have charged 19-year-old Bilal Mumin with murder, grievous bodily harm and possession of an offensive weapon.
Members of the RMT on Arriva Rail North (Northern) walked out for 24 hours, with more stoppages due on Thursday and Saturday.
Police said a dozen shots were fired, but no arrests have been made and they are looking for a dark vehicle.