A tennis player died after waiting more than 40 minutes for an ambulance to arrive in South Yorkshire.
Barry Hodges collapsed at Doncaster Tennis Club after complaining of chest pains, and went into cardiac arrest.
An ambulance was called but did not arrive for 41 minutes, and the 69-year-old was pronounced dead soon after arriving at Doncaster Royal Infirmary.
A coroner has warned more people could die if lessons are not learned from the tragedy.
Louise Slater, assistant coroner for South Yorkshire, said it was not possible to know whether Mr Hodges would have survived had paramedics reached him sooner, but that any delay would reduce the chances of recovery.
She has written to Yorkshire Ambulance Service (YAS) asking it to address concerns arising during Mr Hodges' inquest, which ended on April 20 with a narrative conclusion being recorded.
Ms Slater wrote: "During the course of the inquest the evidence revealed matters giving rise to concern. In my opinion there is a risk that future deaths will occur unless action is taken."
Mr Hodges regularly played tennis and appeared to be in good health when he collapsed at the tennis club on August 23 last year, according to Ms Slater's report.
An ambulance was initially called at 7.12pm but Ms Slater said a series of errors meant that despite four being available at different times, none was sent until after a second call at 7.46pm.
Paramedics eventually arrived at 7.53pm, six minutes after being dispatched, and found Mr Hodges in cardiac arrest and members of the public attempting to perform CPR.
In her report to the chief executive of Yorkshire Ambulance Service, Ms Slater told how the call was not initially coded to show how urgent it was.
When it was coded amber two minutes later the dispatcher failed to review the resources to see if an ambulance was available.
Resources were reviewed at 7.28pm and 7.35pm but no ambulance was allocated despite one being available on both occasions.
The second call was made after Mr Hodges' condition deteriorated. It was this time coded red - the most urgent band - and an ambulance was sent out almost immediately.
Ms Slater said protocols for dispatching ambulances and reviewing resources had not been followed and there was no 'safety net' in place should an individual operative fail to manually refresh and look at the system.
She also said a lack of training and understanding of the protocols meant ambulances were available but not dispatched, and that time scales had been breached without further action such as the matter being escalated to senior management.
The Star has contacted Yorkshire Ambulance Service for a response.
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