Welsh Conservatives today published figures showing 262 cases from last year where an ambulance took over an hour to respond to an emergency call.
The target response time to a life-threatening call is eight minutes.
The Welsh Government is currently undertaking a review into the Welsh Ambulance Services Trust after response time targets were consistently missed.
The Welsh Government’s target of 65% of ambulances arriving at the scene within eight minutes has not been met since May 2012.
Darren Millar AM, Shadow Minister for Health, said, “This figures showing patients in life-threatening situations waiting an hour for paramedics to arrive is simply unacceptable.
“Waiting an hour for an ambulance to arrive causes considerable distress to patients and their families and could even cost lives.
“If someone has a stroke, they need to receive medical attention immediately. Every minute lost can harm their chances of recovery.
“Despite the hard work and dedication of paramedics and other NHS staff, these figures demonstrate that the ambulance service is not delivering the standards patients rightly expect.
“Unfortunately, a lack of investment in the ambulance service, hold-ups in A&E departments and management failings are letting patients down.
“Instead of imposing record-breaking cuts of half a billion pounds to the Welsh NHS and closing A&E departments, Labour Ministers should be investing in the ambulance service and resolving pressures in A&E, which can prevent the smooth and swift transition of patients.
“The Labour Health Minister must ensure that this latest review of the ambulance service addresses patients’ concerns and results in faster response times to allow paramedics to carry out their lifesaving work.”