Pembrokeshire's Conservative Assembly Members have expressed concern that almost half of ambulances responding to 999 calls in the county take more than eight minutes to arrive.
Ambulance response times for Wales as a whole fell to their worst ever level in December.
In Pembrokeshire just 53.6 per cent of 999 calls were answered within eight minutes. The target figure is 65 per cent.
"These figures are very worrying," said Preseli Pembrokeshire AM Paul Davies. "I understand that the Ambulance Service was particularly stretched in December because of an outbreak of a flu-like virus but these outbreaks are going to occur and the service has to be able to cope with them."
In Carmarthenshire only 38.8 per cent of ambulances reached their destination within eight minutes. Carmarthen West and South Pembrokeshire AM Angela Burns added: "What is of great concern to both of us is that ambulances are getting tied up at hospitals when they drop patients off.
"It is taking up to 50 minutes to offload patients and ambulances are getting stacked up outside A&E departments. These bottlenecks are appearing at the hospitals as obviously ambulance crews can't respond to emergency calls if they still have a patient on board. We need to see closer co-operation between hospitals and the ambulance service to address this. I have written to the Welsh Ambulance Service to request a meeting to discuss these delays and other matters."