John Radcliffe Hospital is investigating the deaths of four children who underwent heart operations there in recent months.

The Oxford hospital has suspended children’s cardiac surgery until the investigation has been concluded.

Our investigations are likely to include an external review of the deaths of some very sick children

Parents of 26 children due to undergo operations at the children’s hospital based there are currently being contacted. Those who need urgent treatment are to be transferred elsewhere.

The deaths of the “very sick children” happened either during or after surgery. The hospital is yet to release further details about the fatalities.

A spokesman for Oxford Radcliffe Hospitals Trust said: “We have temporarily suspended the paediatric cardiac surgery service while we investigate concerns that have been raised.

“Our investigations are likely to include an external review of the deaths of some very sick children (four children) who underwent surgery at the John Radcliffe Hospital in the last three to four months.

“The families of children awaiting cardiac surgery are being contacted and we will be placing those patients who need to be seen urgently with other hospitals.

“We are reviewing each of these patients to ensure that they are not put at risk by any delay in their treatment.”

Deaths after children’s heart surgery at the hospital fall within normal ranges and there has been no previous cause for concern.

The Care Quality Commission said it was monitoring the situation closely.

Society of Cardiothoracic Surgery president Leslie Hamilton said children needing heart surgery would be sent to one of the country’s 10 other specialist units while the Oxford service is suspended.