Almost half of all ambulances here are failing to arrive to the most seriously ill patients within the target time.
It is now nearly a year since the targets were last hit.
Opposition parties have called for 'immediate action' to improve response times, whilst the Welsh Government has admitted the situation as unacceptable.
The target for 'immediately life-threatening' calls is for 65 percent of ambulances to arrive at the scene within eight minutes
In March 2013, only 53.3 percent arrived at the scene within eight minutes
The figures for March show that the national target for 65 percent of ambulances to respond to calls for 'immediately life-threatening' cases within eight minutes was missed in every local council area in Wales.
It drops to 42.1 percent in Rhondda Cynon Taf, and 43.5 percent in Merthyr Tydfil.
Ambulances arrived within eight minutes for Pembrokeshire, Wrexham, Conwy and Denbighshire between 60 and 65 percent of the time.
The Welsh Conservatives have called for "immediate action" from the Welsh Government to address how failings over ambulance response times.
The Welsh Liberal Democrats have described the Welsh Government's failure to address ambulance response times as "an absolute disgrace".
They have highlighted how targets here in Wales are already 10 percent behind England and Scotland, but are still not being met.
Plaid Cymru says the figures showing a tenth successive month where ambulances failed to meet their response-time targets highlights that the NHS "is at crisis point."
The Welsh Government commissioned a review into the Welsh Ambulance Service last November.
The Health Minister now has the findings of that review, which will debated in the Senedd on 7 May.
A Welsh Government spokesperson said: "The Health Minister Mark Drakeford is aware of the pressures on unscheduled care and the impact this is having on emergency ambulance performance."
"During his statement in the Senedd yesterday, he outlined short, mid and long-term plans to tackle the matter, which includes implementing immediate actions to reduce ambulance handover times at A&E departments."