British scientists are stepping up clinical tests of gene therapy in a bid to help people with advanced heart failure pump blood more efficiently.

Researchers said on Tuesday they planned to enrol patients into two new clinical trials using Mydicar, a gene therapy treatment made by privately held U.S. biotech company Celladon.

After more than 20 years of research, the ground-breaking method for fixing faulty genes is starting to deliver, with European authorities approving the first gene therapy for an rare metabolic disease last November.

In the case of heart failure, the aim is to insert a gene called SERCA2a directly into heart cells using a modified virus, delivered via a catheter infusion. Lack of SERCA2a leads to ever weaker pumping in people with heart failure.

Although drugs offer some relief, there is currently no way of restoring heart function and the prognosis for those with advanced disease is worse than for many cancers.

One of the studies, led by scientists at Imperial College London, is part of a wider mid-stage Phase II project sponsored by Celladon that involves 200 patients worldwide, some of whom have already been treated in the United States and Denmark.

The second trial, which is due to start in the summer, will test the same treatment in 24 British patients already fitted with mechanical heart pumps to see how the approach may help in this particular setting.

It promises to be a long haul, with extensive Phase III studies still needed once results of the current mid-stage tests are received, which Celladon expects in the first half of 2015.

Gene therapy has experienced a series of advances and setbacks over the decades. The most notable blow came in 1999 when an Arizona teenager died in a gene therapy experiment. More recent results, however, have been promising in fields ranging from immune system diseases to blindness.

"It is a great example of the slow burn of good laboratory science translating into a potential clinical treatment," said Peter Weissberg, medical director of the British Heart Foundation, which is co-funding the second trial.

Because gene therapy replaces or boosts the activity of a faulty gene, it offers the possibility of a one-time "fix" - and that creates an economic challenge.

Any gene therapy is bound to be expensive, since a single dose could last a lifetime and the manufacturer will have just one shot at recouping its investment.

But Alexander Lyon of Imperial College, lead investigator on both studies, said it could be a cost-effective solution in heart failure if it avoided the need for interventions such as heart transplants at 200,000 pounds ($300,000) each.