Equipment failures and other response problems are highlighted in data outlining patient deaths in botched emergency callouts.
In some cases, defibrillators did not work properly and in others there were delays and wrong information.
St John Ambulance's report to the Ministry of Health for the 12 months to the end of March shows 30 so-called reportable events.
Patients died in many cases. In one, a patient died before an ambulance arrived when the call wasn't properly taken.
In another case, staff could not find an address and the patient died before they got there. And in another response, a wrong priority was assigned to a cardiac arrest.
The information shows problems with defibrillators. The device malfunctioned in once instance, and while a second ambulance arrived within minutes, the patient did not survive.
St John says new systems will help cut down on delays in cases where ambulance response time is crucial.
Chief executive Peter Bradley says any delay is one too many - but they do happen. He says a new system that started this year gives calls where patients are not breathing or are in cardiac arrest absolute priority.
Mr Bradley says the 30 reported cases are from about 400,000 St John responses over the year. He says there is no trend shown when compared with earlier results.
St John ambulance service covers all but Wellington, Kapiti and Wairarapa - which is covered by the Wellington Free Ambulance.
