Doctors will randomly treathalf the patients with a harmless virus carrying a corrective gene. The restwill receive an inactive placebo treatment.
Previous research suggests that a protein produced by the gene can restore function to failing hearts, and reduce the risk of death and heart transplants.
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Pictures of today's events unfolding following a major security incident at the Houses of Parliament.
At least two people have died after a knifeman brought terror to the heart of Westminster.
The Cobra committee brings together government ministers with senior officials of the emergency services and security agencies.