The Royal College of Physicians said the East Midlands Ambulance Service (EMAS) had failed to meet targets for administering the drugs.

Ambulance bosses said staff are trained but the drug was not suitable for all.

Figures show 51% of patients in Nottingham, 48% in Derby, 39% in Leicester and 49% in Lincoln receive the drug within an hour.

'Early days'

The sooner the thrombolytic drug is given, the more effective it is and the greater chance the patient will make a full recovery.

If the clot is not cleared, the heart will suffer permanent damage, the report said.

It's a new procedure for the paramedics and a learning curve for them Peter Ripley, assistant director of operations at EMAS

Nationally, 55% of patients received the treatment within an hour of calling for professional help, from medical staff such as ambulance crews, NHS Direct or GP services.

All EMAS paramedics are now able to administer the drug, following a training programme over the past year.

Peter Ripley, assistant director of operations at EMAS said: "It is still very early days for us.

"It's a new procedure for the paramedics and a learning curve for them.

"At the moment we need to reduce the time it takes to make an assessment of the patient so there can be fewer delays on scene and so patients can be treated more quickly.

"I am confident we can do this as the time goes on."