On two occasions this year, it took an ambulance more than 60 minutes to arrive at a life-threatening emergency, according to Ambulance Service data.
New figures also show that response-time targets are not being met in up to 50% of such cases across the country.
Hiqa said ambulances should arrive at life-threatening emergencies in less than 19 minutes in 80% of cases.
However, new figures released by the National Ambulance Service, show this is not being met in almost all regions in Ireland.
In the first four months of this year, for non-cardiac cases, it was reached only 44% of the time by Dublin Fire Brigade, the major provider of emergency ambulance cover in Dublin.
It was also met in only 52% of these type of cases in the west and southeast.
There were response-times of over an hour in Kildare and Cork and one of 44 minutes in Leitrim – and three further calls of over 42 minutes for cardiac emergencies, in Tipperary, Monaghan and Wexford.
David Hall, who runs Lifeline Ambulance, a private firm, said it is a major concern.
He said: “These statistics that are being published that in some parts of the country [that response-time targets being met] are down as low as 50% are absolutely horrific. These are people’s lives, people who are in grave danger in an emergency situation and the Minister must act urgently to ensure proper resources.”
The HSE has not yet responded to requests for comment on the statistics.