Scientists are testing a drug that can mend a broken heart.

Experiments found the medicine, which is usually used to treat cancer, shrank enlarged and diseased hearts back down to near normal size, allowing them to work properly again.

Now the drug is about to be given to human heart patients for the first time.

In the future, it could be used to prevent and treat heart failure – one of the biggest causes of hospital admissions and death.

The drug’s powerful effect could provide a godsend for some of the millions worldwide suffering from heart failure, in which a weakened heart struggles to pump blood around the body.

Caused by heart attacks, high blood pressure and other conditions, more than 750,000 people live with it in the UK alone, with everyday tasks such as eating, dressing and getting out of bed leaving many sufferers breathless and exhausted.

Treatments range from drugs to transplants but with up to 40 per cent of those affected dying within a year of diagnosis, it has a worse survival rate than many cancers.

The medicine tested belongs to a family of drugs called histone deacetylases, which are already used to treat tumours.

But research from the University of Texas’s Southwestern heart centre shows that they also temper autophagy, a process in which cells eat their own proteins.

Autophagy allows cells to tidy up unwanted debris. But when it gets out of control, too many vital parts are eaten and the cells die.

In hearts, this can further damage those which are already diseased.

The researchers gave the drug to mice with high levels of autophagy and enlarged hearts that could fail, with incredible results.

Joseph Hill, the heart centre’s chief of cardiology, said: ‘The heart decreased back to near its normal size, and heart function that had previously been declining went back to normal. That is a powerful observation where disease regression, not just disease prevention, was seen.’

He hopes the drug could be used to repair hearts damaged by heart attacks and other forms of disease.

Dr Hill told the Daily Mail: ‘There is a huge need for new treatments for heart failure.

‘The final common pathway for most types of heart disease, high blood pressure, heart attacks or valve disease is heart failure and it is sky-rocketing.’

He is about to start small, preliminary tests on heart patients. If successful, larger-scale trials will follow.

The tests that led to the breakthrough began ‘decades ago’ on yeast, said the researchers, but only now does it seem likely it can be adapted to the human heart.

Dr Hill said: ‘This is one of those exciting, but rare, examples where an important finding made originally in yeast moved into mouse models and is soon moving to humans.’

The approach is one of several being explored around the world.

The British Heart Foundation wants to raise £50million within five years to fund research into repairing hearts.

Launching the appeal earlier this year, Professor Peter Weissberg, the BHF’s medical director, said: ‘Scientifically, mending human hearts is an achievable goal and we really could make recovering from a heart attack as simple as getting over a broken leg.’

Last night, Professor Jeremy Pearson, the charity’s associated medical director, said: ‘This is an intriguing study which suggests that an anti-cancer drug can, unexpectedly, be beneficial in heart failure – a condition which urgently needs new medicines to help treat it.’