Ambulance crews are failing to regularly reach patients within the time limit demanded by the Government.
Crews are expected to answer 75 per cent of life-threatening emergency calls within eight minutes.
In the period April to December 2002, Sussex Ambulance Service recorded an average response time of 73 per cent.
Ambulance bosses said that in the past 18 months, there had been an increase in the number of incidents crews had to deal with.
It has spent £1.65 million on several measures, including new fast-response vehicles and extra staff to help improve times. The average rate in 2001 was about 70 per cent.
Crews regularly deal with more than 450 incidents a day with the number rising to more than 500 at peak times.
Ambulance service chief executive David Griffiths said: "We are continuing with our performance improvement programme and have achieved most of what we have set out to do.
"Now we have to work on that to try to consistently reach the target we need but we are nearly there."
Chairman Patrick Herbert said: "We are dealing with many more calls than in previous years and, despite this, crews are still managing to do extremely well. Everything possible is being done to reach the target."
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