The director of the National Ambulance Service has said he is taking "very seriously" figures that show wide geographical variations in emergency response times.
Less than half of cardiac call-outs in the west of Ireland are responded to within the recommended 19 minutes set down by Health Information and Quality Authority.
Roscommon-South Leitrim TD Denis Naughten received the information after he submitted a parliamentary question to Minister for Health James Reilly.
Speaking on RTÉ's Morning Ireland, Martin Dunne said the service was introducing new vehicles to deal with non-emergency cases and lessen the burden on larger ambulances, as well as streamlining its command and control centres.
He said: "The response time set down by HIQA require us to have a vehicle in place by 19 minutes - or 18 minutes 59 seconds to be exact - and in certain areas of the country, it has been highlighted to us that we're not meeting those targets.
"We're looking at that very seriously and we're putting several mechanisms in place, I assume, to make sure that we start meeting these targets."
Poor weather and bad road infrastructure were problems when accessing rural areas, Mr Dunne said.
However, he said traffic gridlock was also an issue in accessing emergencies in urban areas.
He said the service was currently going through "huge change" in order to improve response times, but declined to give a timeframe for when the Ambulance Service would meet the 19-minute target across the country.
Mr Dunne said he was happy with the number of ambulances and the current level of Health Service Executive funding at his disposal.