Researchers in the US performed the feat using human cells in a laboratory dish.
They "reprogrammed" scar-forming fibroblast cells into the building blocks of beating heart muscle by injecting them with a cocktail of five genes.
Previously, they did the same in living mice using a three-gene combination.
Study leader Professor Deepak Srivastava, from the University of California in San Francisco, said: "Fibroblasts make up about 50% of all cells in the heart and therefore represent a vast pool of cells that could one day be harnessed and reprogrammed to create new muscle.
"Our findings here serve as a proof of concept that human fibroblasts can be reprogrammed successfully into beating heart cells."
While most of the cells showed at least a partial transformation, a fifth of them were capable of transmitting electrical signals - a key feature of beating heart cells, the scientists writing in the journal Stem Cell Reports said. Success rates might be improved by transforming fibroblasts in living hearts rather than a dish, they suggested.
"Our findings... come at a critical time," Dr Srivastava said."We've now laid a solid foundation for developing a way to reverse the damage -something previously thought impossible - and changing the way that doctors treat heart attacks in the future."