The devastating effects of a heart attack or stroke could be reduced by more than half by a simple injection, a study suggests.
British scientists are developing a treatment they say could reduce scarring in the heart and brain by more than 60 per cent.
The drug has been tested on mice and other mammals - but has also on human blood in a laboratory.
Researchers hope to begin human trials of the drug, developed at Leicester University, within two years.
Its key ingredient is an antibody, which could be administered up to 12 hours of the attack to stop damage to cells.
It helps heart attack victims by preventing the body attacking its own oxygen-starved cells.
Professor Wilhelm Schwaeble, an immunologist who carried out the work, said the findings had the potential to be the ‘biggest breakthrough ever’ in treating victims of the two biggest killers in Britain.
It could also be used to stop the body attacking organ transplants.
‘This is potentially the biggest breakthrough in the treatment of heart attacks and strokes ever,’ Prof Wilhelm told a national newspaper.
‘We could not believe what we saw and nor could the cardiologists. What is amazing is that the drug can be given so long after the attack.
‘Even the slowest ambulance journey in the world is going to get you to hospital within nine hours.’
Strokes and heart attacks are caused by a clot or a bleed which blocking the blood flow, causing other parts of the body to be starved of oxygen.
However, the worst damage is caused around nine to 12 hours afterwards, when circulation returns to normal but the body’s immune system attacks the oxygen-starved cells.
This causes inflammation and accounts for more than 80 per cent of the permanent damage – often leading to death or serious disability.
Scientists claim the injection stops the body attacking oxygen-starved cells – allowing them to oxygenate normally and therefore reducing permanent damage.
Prof Wilhelm added that the drug could have even more of an effect than the widely-used statins, which lower cholesterol.
The research, published in the Proceedings of the National Academy of Sciences (PNAS), centred around a protein called OMS646.
It was found to knock out MASP-2, enzyme responsible for the immune attack, and is so effective that only two injections would be needed.
Cardiovascular disease, including heart disease and stroke, claims the lives of around 200,000 British people every year.