"Researchers at Karolinska Institute have now shown that human heart cells undergo continual, slow replacement," the Swedish institute said in a statement.
Scientific research has shown that some of the body's cells are renewed each week while others are never replaced. A long debate has simmered over whether the heart's cells are replaced, with most cardiologists convinced until now that they are not.
In a 20-year-old one percent of heart cells are renewed every year, a rate that gradually declines over the years to reach 0.5 percent in a 75-year-old, it said.
"We lose heart cells naturally, and most of those are replaced. But you can also lose millions of cells from a heart attack or illness," Jonas Frisen, the professor who led the study, told AFP.
"Our results motivate further research into ways of stimulating the renewal mechanism," he said.
In the event of a heart attack or illness, the slow rate of turnover means that most heart cells are never replaced, "leaving the heart a patchwork of cells that have been there from birth and cells that have been formed later in life".
The researchers therefore used a unique method to determine how old the cells were.
Nuclear tests during the Cold War produced a sharp increase in atmospheric concentrations of radioactive carbon-14, which is stored in the body's cells.
"Since levels have varied over the past decades, they serve as an indicator of when the cells were formed," Karolinska Institute said.
The study was published in Friday's edition of US journal Science.