Three men who had heart failure caused by a build-up of toxic proteins have seen their condition spontaneously reversed in what has been described as “an unprecedented case”.

Cardiac amyloidosis is a progressive condition which until now was seen as irreversible.

It is caused by a build-up of abnormal proteins, known as amyloids, in heart tissues and affects its function.

Scientists from University College London (UCL) and the Royal Free Hospital performed medical tests on the men, aged 68, 76 and 82, after reports that their symptoms were improving.

Scans showed amyloid protein deposits had cleared from their hearts.

The researchers also found evidence of antibodies – protective proteins produced by the immune system – that specifically targeted these amyloid proteins.

These antibodies were not found in other patients whose condition progressed as normal, they said.

The hope is that the findings, published in the The New England Journal of Medicine, could lead to new treatments for the condition.

We have seen for the first time that the heart can get better with this disease

Lead author Professor Marianna Fontana, of UCL Division of Medicine, said: “We have seen for the first time that the heart can get better with this disease.

“That has not been known until now and it raises the bar for what might be possible with new treatments.”

For the study, the researchers looked at a specific type of cardiac amyloidosis, known as transthyretin ATTR amyloid cardiomyopathy (ATTR-CM), caused by amyloid deposits of a blood protein called transthyretin (TTR).

The prevalence of ATTR-CM in the UK is currently unknown due to potential under-diagnosis and under-reporting of the condition.

It is a chronic disease that gets worse over time and can be potentially fatal.

The researchers looked at the records of 1,663 patients with the condition after one of the men, aged 68, reported his symptoms improving.

Two more cases were identified and confirmed through blood tests, scans and medical imaging techniques.

The team found antibodies in the three patients that bound specifically to ATTR amyloid deposits in mouse and human tissue in the lab.

The researchers said that harnessing these antibodies could help clear away amyloid and potentially reverse the condition.

Scientists led by Professor Julian Gillmore, of UCL Division of Medicine, are investigating a gene-editing therapy that could stop cardiac amyloidosis from progressing.

Early results of the trial indicate it may stop disease progression, the team said.

Prof Gillmore, who is also head of the UCL Centre for Amyloidosis based at the Royal Free Hospital, said: “Whether these antibodies caused the patients’ recovery is not conclusively proven.

“However, our data indicates that this is highly likely and there is potential for such antibodies to be recreated in a lab and used as a therapy.

“We are currently investigating this further, although this research remains at a preliminary stage.”

Jon Spiers, chief executive of the Royal Free Charity – which supported the study, said: “This work not only represents a major breakthrough in our understanding of cardiac amyloidosis, but crucially opens up new possibilities for more effective treatment options.”