Doctors at the London Chest Hospital have started treating heart attack patients with their own stem cells.
The London patients are among the first of 3,000 participants in the European-wide study to look at the life prolonging effects of stem cell therapy.
Five days after suffering a heart attack, stem cells will harvested from the patient's own bone marrow and then be injected into heart muscles in the hope that they repair some of the damage.
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The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.