There are calls for a "serious investigation" after shocking new figures have revealed more than 200 cases across Wales last year when an ambulance took over an hour to reach the most critical calls.
In one 999 case, paramedics took almost two hours to respond to a reported stabbing or shooting - and a patient with a suspected heart attack had to wait more than three hours.
The delays only came to light after the Shadow Health Minister demanded the figures under the Freedom of Information Act.
Our Health Reporter Rob Osborne has our top story.
Rhian Jones' ex-husband Michael had a serious stroke in her house in 2010, and the ambulance took two hours to arrive.
She told our Health Reporter Rob Osborne it was simply "frightening" waiting for paramedics to arrive, and her confidence in the emergency care system has been shaken as a result.
– Welsh Ambulance Service spokesperson
The Health Minister has commissioned a review of Welsh Ambulance Service which will include specific focus on how improvements can be achieved in the responsiveness of the emergency ambulance service. The Welsh Ambulance Service will continue to work closely with Local Health Boards and the Welsh Government to achieve improvements.
The Shadow Health Minister Darren Millar described the figures about ambulance response times in 2012 as "shocking" and "inexcusable".
He said "we have a big problem in the way that our emergency care system is operating in Wales", both in terms of ambulances and A&E departments.
The Welsh Government has commissioned a review into how emergency response times can be improved, which will report next month.
The Shadow Health Minister, Darren Millar has called for a 'serious investigation' into ambulance responses to 999 calls.
Figures he obtained under the Freedom of Information Act show 262 emergencies in Wales last year where the wait for an ambulance was over an hour and it took nearly two hours for an ambulance to reach a stab or gunshot incident.
– Shadow Health Minister Darren Millar AM
We do not know what the outcomes in each of those cases are, whether people have died needlessly because an ambulance has not turned up. I think there needs to be a serious investigation into what has gone on in each of these cases.
The Health Minister is well aware of the challenges facing the ambulance service in Wales and recognises performance needs to improve, which is why she ordered a review of the service last November.
The review will conclude at the end of March, with a report to the Minister to follow shortly after.
– Welsh Government spokesperson
The review will consider how emergency response times can be improved. In the meantime, the Minister expects the Welsh Ambulance Services NHS Trust to continue to work closely with Local Health Boards to provide safe emergency services that meet the clinical needs of patients.
Performance should be seen in the context of wider pressure on the NHS emergency care system and rapidly increasing demand, including a 6% increase in calls categorised as life threatening since September 2012.
Figures released under the Freedom of Information Act reveal there were more than 250 category A emergency calls to the Ambulance Service in Wales last year where people had to wait over an hour for paramedics to arrive.
In one 999 call involving an incident categorised as a stab or gunshot in Blanaeu Gwent, it took emergency staff almost two hours to arrive.
In January, figures showed the Welsh Ambulance Service failed to meet its target response time for urgent cases for the seventh successive month.