Heart failure results after damage to the heart muscle causes it to deteriorate, which in turn progressively weakens cells that govern heartbeat. The result is serious fatigue due to the heart’s inability to pump blood efficiently. Each year in the UK alone it affects 120,000 people who have never had the condition before, killing a third of them within 12 months. Doctors will inject participants with harmless viruses that ferry a gene called SERCA2a into their heart muscle. The gene codes for a protein that recycles calcium within heart muscle cells, vital for driving each heartbeat and priming the next one. In damaged cells, this recycling is impaired. By loading new copies of the gene the aim is to compensate for this decline.”