It took over four hours for an ambulance to arrive at a life-threatening emergency call 94 times last year.
According to Freedom of Information figures, released to Newstalk, 21 of these were over five hours.
The HSE aims to respond to life-threatening heart and respiratory calls within 18 minutes and 59 seconds in 80% of cases.
Other life-threatening emergencies should be responded to within the same timeframe in 50% of cases.
On almost 6,200 occasions last year, it took over an hour for an ambulance to respond to either of these types of calls.
The longest was almost seven hours and 10 minutes to a call in Waterford.
That was followed by over six hours to calls in Cork and Westmeath.
A total of 233 response times were over three hours.
'Very worrying and concerning'
David Hall is the chief executive of Lifeline Ambulance Service.
"HIQA now need to have a look at the clinical outcome of those calls, to see were there any adverse clinical outcomes upon the patients who were left waiting so long," he said.
"By definition these are patients who are very, very sick.
"To have so many people waiting so long would be very worrying [and] very concerning.
"You wonder whether clinical outcomes are put in jeopardy as a direct result of those delays?
"That's the real way that this needs to be evaluated properly, and the appropriate measures and steps need to be taken to protect lives," he added.
The Oireachtas Health Committee will discuss ambulance services - including response times - with the National Ambulance Service and Dublin Fire Brigade later this morning.