Figures revealed by the Welsh Liberal Democrats in RCT show that one in six of the ambulance call out in the Cwm Taf area which covers Rhondda Cynon Taff and Merthyr are to locations outside of that area.
During the six months between June and December last year 4,523 ambulance call out were made to other Health Board areas including journeys to Monmouthshire of 40 miles or more.
Welsh Liberal Democrat Parliamentary candidate for Pontypridd Mike Powell says it is one of numerous background reasons why the response time in Cwm Taf area regularly at or near the bottom of the league table.
"The MP for the Rhondda pointed out a couple of weeks ago that there were a significant number of ambulance being used to make calls in Cardiff following drop offs at the Heath hospital, but in fact the problem is much more far reaching.
"We have from the ambulance service a list of call outs to each post code area and the overall picture is quite worrying. It includes journeys from Pontyclun and Gelli to Monmouthshire of over 40 miles each way and numerous call outs to areas of Swansea as well as to Llandrindod Wells and Brecon.
"Is it any wonder that the target is not being hit in RCT when our response vehicles are being used to cover gaps in the service elsewhere?"
A series of Freedom of Information requests by RCT Welsh Liberal Democrats also revealed the startling levels of sickness and absence in the service. In the Cwm Taf area the equivalent of 6516 days were lost due to sickness and across Wales the figure amounted to 64,304 days.
Campaign Manager Karen Roberts says it is a measure of the strain staff are under
"The front line staff are being put under tremendous pressure to meet targets and morale must be at rock bottom given the constant failure to do so. Yet there are so many elements out of their control such as insufficient resources both of staff and equipment and over long hand over times at A&E.
"As a result - as with our nursing staff - we are seeing high incidences of sickness often as a result of stress. Something needs to be done, we have had enough service reviews it is time we saw some concrete changes."