It has taken an ambulance at least an hour to arrive at a life-threatening emergency more than 120 times this year.
On one occasion, it was nearly four hours before a patient was attended to.
According to guidelines from the Health Information and Quality Authority, an ambulance should arrive at life-threatening emergencies in less than 19 minutes in 80% of cases.
But new figures, released under the Freedom of Information Act, show this target is not being met in some cases.
On 123 occasions in the first nine months of this year, it was more than an hour before an ambulance arrive.
Stephen McMahon from the Irish Patients Association said: "It is a cause for concern and we would hope that the National Ambulance Service would be reviewing each and every case that is outside the safety of 19 minutes."
Of the response times of more than an hour, 26 were in Wexford, followed by 20 in Cork and 13 in Kerry.
Speaking as a Wexford Independent councillor, paramedic Ger Carthy said it is a big worry for the area's growing population.
Cllr Carthy said: "Wexford is predominantly a tourist destination for four months of the summer and our population increases by around 50,000.
"But I suppose, unfortunately, the National Ambulance Service can't be at every corner to respond to those calls. It is somewhat concerning."
Nine times this year, it took at least an hour for an ambulance to arrive at a life-threatening emergency in Mayo, one of which was three hours and 50 minutes, which was the worst in the country.