East Midlands Ambulance Service (EMAS) failed to reach thousands of patients in rural parts of Derbyshire in 2013 within the target time, figures show.
EMAS is supposed to reach 75% of serious cases within eight minutes.
But in areas around Matlock, Ashbourne, Swadlincote and Bakewell, figures suggest the service failed to reach even 50% of people within that time.