A new pacemaker has been built inside a heart by converting beating muscle into cells which can organise the organ’s rhythm, US researchers report.

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They used a virus to infect heart muscle cells with a gene, called Tbx18, which is normally active when pacemaker cells are formed during normal development in an embryo.

When heart cells were infected with the virus they became smaller, thin and tapered as they acquired the “distinctive features of pacemaker cells”, the report said.

When the virus was injected into a region of the hearts of seven guinea pigs, five later had heartbeats which originated from their new pacemaker.

Researchers working on a foam designed to limit internal bleeding of soldiers injured on the battlefield have received $15.5m (£9.6m) from the US military to continue their work.

The virus used in the research was an M13 bacteriophage, which attacks bacteria but is benign to humans. The Berkeley team used genetic engineering techniques to add four negatively charged molecules to one end of the corkscrew-shaped proteins that coat the virus.

These additional molecules increased the charge difference between the proteins’ positive and negative ends, boosting the voltage of the virus.

Another advantage of using viruses for such tasks is that they arrange themselves into an orderly film that enables the generator to work. This attribute, known as “self-assembly” is much sought after in the field of nanotechnology.