An investigation has been launched after two men in South Australia died on Monday while waiting for ambulances to arrive.
The Ambulance Employees Association (AEA) said there were not any ambulances available at the time to attend the priority one and two call-outs for cardiac-related issues.
By the time paramedics arrived, the patients had died in both instances.
The SA Ambulance Service (SAAS) has expressed its "sincere condolences to the loved ones", and has launched a review.
AEA general secretary Leah Watkins said she was "so angry" about what had occurred, describing it as "devastating" for the families involved and the paramedics who responded.
The first case occurred at Modbury Heights early on Monday morning, when a man went into cardiac arrest and a family member called triple-0.
The union said it should have taken seven minutes to respond to the priority one case — but it took 14, and the man could not be revived.
The second episode happened last night when family called triple-0 "for their loved one with chest pain, struggling to breathe".
"There was no ambulance to send immediately, again," Ms Watkins said.
"About 20 minutes later the family member called back to say the patient had gone into cardiac arrest.
"That ambulance arrived over 30 minutes — nearly 35 minutes — after the triple 0 was received and that patient was also tragically unable to be revived."
SAAS conceded the response times were unacceptable.
"SAAS offers sincere condolences to the loved ones of both patients during this extremely upsetting time," SAAS said in a statement.
The union has linked the incidents to ramping, and Labor leader Peter Malinauskas lashed out at the SA government over the revelations, claiming it as evidence that ramping is escalating.
"There's an investigation underway, what we know is that we need to end ramping in SA [and] there's only one party that is taking a comprehensive plan to this upcoming election," he said.
SAAS added that it continued "to implement measures where possible to enhance patient care and improve our response times".
