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Ten heart patients were on Capital and Coast District Health Board's (DHB) waiting list for cardiac surgery when there were three "preventable" deaths, Health Minister David Cunliffe said today.

Capital and Coast DHB had advised him 10 patients had been on its waiting list for cardiac surgery," he said.

"It has been alleged...that three deaths were preventable and I have asked the director-general of health to mount an urgent, independent investigation to ascertain the veracity of those claims."

Mr Cunliffe announced this inquiry at the beginning of this month but Opposition MPs took the oppoortunity of the return of Parliament to question the Government's record on waiting lists.

Act MP Heather Roy today asked if Mr Cunliffe stood by his government's promise that patients who met the treatment threshold of 50 points and had "certainty of treatment" would get their surgery within six months.

"... whose fault is it that Capital and Coast District Health Board has failed to honour this promise for 70 patients whose lives have been put at risk and indeed resulted in an least three needless deaths," Mrs Roy said.

She released papers she obtained under the Official Information Act that showed last October there were about 90 patients - who had been told they would get surgery - but had waited more than six months for their operations.

Mr Cunliffe said the Wellington DHB was working on an urgent recovery plan to reduce the waiting list.

The DHB was conservatively projecting the waiting list would be reduced by 50 per cent by July this year and that it would reduce those waiting over six months to almost zero by the end of the year.

Mr Cunliffe said he shared concerns that at some DHBs, patients were waiting longer than six months for surgery.

National health spokesman Tony Ryall said the heart surgery waiting list at Wellington Hospital had "trebled"' since Labour came to office, while the amount of heart surgery there had "flatlined" in recent years.

He asked the minister to explain why in some weeks at Wellington Hospital, more cardiac operations were cancelled than were performed.

Mr Cunliffe said it was the responsibility of DHBs to manage individual clinical services.

The DHB was "not funding constrained" regarding its cardiac waiting list, he said.

"The Government has provided the funds. We are working with the CCDHB to remove the bottlenecks."

Mr Cunliffe said a replacement cardiothoracic surgeon was starting in just over a month's time.

The DHB had now increased the number of operations to about 60 a month.

Last year, the DHB was performing nine cardiothoracic elective procedures a week but was increasing this to about 16 per week.