Babies born with heart problems develop their deadly defect long before the organ has even begun to form, much earlier than scientists realised.
Breakthrough research by leading Australian scientists has changed the understanding of how congenital heart problems, like hole in the heart, begin.
While therapies to stop children developing defects are still some way off, the Victor Chang Cardiac Research Institute team says its findings could benefit adults with heart issues.
The scientists found that congenital heart problems take hold very early in very immature cells, called progenitor cells, that only later become the heart.
"Previously it was believed that heart defects ... originated as the heart was forming," said professor Richard Harvey, head of the Sydney-based institute's developmental biology program.
"The work we conducted has shown that these problems can actually result from much earlier defects in the heart progenitor cells that only later develop into the heart."
Congenital heart defects are responsible for more deaths in the first year of life than any other birth defect, yet for most there are still no therapies to treat these problems apart from major open-heart surgery.
The findings, published in the international biomedical journal Cell, relate to a gene called Nkx2-5, which is vital in heart development.
It is the most common single gene involved in congenital heart disease, making it an important target for new research in the field.
Defects in the Nkx2-5 gene slow the production rate of new heart cells from the progenitor cells.
"This leads to problems such as a hole in the heart, incorrect positioning of major vessels such as the aorta, and heart valve problems," said Dr Owen Prall, who led the study.
He said this work advanced the understanding of how certain heart defects occurred.
The findings won't immediately benefit children but adults were set to gain from them.
"It is now known that adult hearts also contain small numbers of heart progenitor cells," Dr Prall said.
"In the near future we may be able to aid people who have experienced heart failure, by boosting the number of these cells so that damaged muscle can be repaired."