Latest figures showing how well the Welsh Ambulance Service responded to 999 calls will be published later today.
It will show response times for December 2014 - an extremely busy time for the health boards right across the country.
The target, set by the Welsh Government, is for 65% of the most serious calls (Red 1 or Red 2) to be responded to by an ambulance within eight minutes.
November was the worst month since 2011. Only 51% of ambulances in reached the most life threatening calls within the set target.
The figures for December are expected to be even worse.
A review published in 2013 highlighted a number of challenges for the Welsh Ambulance Service in its ability to achieve the eight minute target.
As well as increasing demand on the service, challenges included the number of rural and sparsely populated areas in the country, making it difficult for paramedics to predict the 'focus of demand'.
Winter driving conditions was also noted as being challenge where dangerous weather can result in reduced speed.
The report also highlighted lengthy patient handover delays at emergency departments as being a problem for ambulances to respond to their next call within the set target.
You can also watch a report how one health board is trying to relieve pressure at A&E by sending emergency consultants out on the road with paramedics:
On Wales at Six tonight, our Health and Social Affairs Correspondent Rob Osborne will be questioning the point of the eight minute target and whether it's effective for paramedics to reach on the road.