The head of an ambulance trust has apologised for serious delays in reaching potentially seriously ill patients.
Hayden Newton, the chief executive of the East of England Ambulance Service, said the trust had implemented an action plan to improve response times.
He also acknowledged patients in rural areas had been receiving "a second class service".
It comes after an investigation by BBC Look East disclosed the number of heart and stroke patients waiting more than an hour for an ambulance to take them to hospital had quadrupled in the past three years.
The ambulance trust's own figures, obtained by the BBC, show that in 2010-11, there were 351 occasions where a vehicle called to a patient with a suspected stroke or heart problem took more than an hour to arrive on scene.
This is up from 72 in 2007-08.
Mr Newton said: "We need to do better. There is a process of continuous improvement in terms of those people who live in the more rural parts of the patch.
"I recognise the importance of getting there quickly to a small group of patients who need rapid intervention and high quality care.
"I'm very sorry. Things will improve".
His comments followed a meeting with two east of England MPs who had raised concerns.
Liberal Democrat North Norfolk MP Norman Lamb said: "The current performance is unacceptable, particularly in rural areas - too many people waiting too long to get an ambulance to hospital and that's intolerable."
Conservative MP for Central Suffolk and North Ipswich, Dr Dan Poulter said: "The ambulance service has accepted at the moment there is effectively a second class service for more rural areas and rural counties like Suffolk, Norfolk and Cambridgeshire."