A gene that seems to hold the key to causing an enlarged or "heavy" heart has been identified by British researchers.
The gene causes the heart muscle to thicken, raising the odds of potentially fatal heart failure.
The finding could pave the way for new treatments that target the underlying causes of heart conditions rather than just treating the symptoms.
In heart failure, the weakened heart struggles to pump blood round the body, meaning that everyday tasks such as eating, dressing and getting out of bed can leave people breathless and exhausted.
Even sitting still in a chair can leave those worst affected gasping for breath.
In experiments on mice and rats, the researchers from the Imperial College London showed a flaw in a gene called Endog to be linked to the thickening of the heart wall and a reduction in the amount of blood it is able to pump round the body.
"Our study shows that the Endog gene, which was previously thought to be involved in cell death, actually plays an important role in the enlargement of the heart, which can lead to heart failure and eventually death in the worst cases," the Daily Mail quoted study leader Professor Stuart Cook as saying.
"We found that a faulty copy of this gene causes the heart to become thick and fatty, making it "heavy" with poor function," he said.
Prof Cook said that the gene does this by interfering with the heart cells' energy source - the mitochondria.
"Like any other muscle in our body, the heart needs energy to keep it pumping," he said.
"If the mitochondria don't work properly, the heart struggles to make enough energy and the cells produce toxic by-products, which increase thickening of the heart wall," he added.
The researchers are optimistic that the gene is also key to heart health in people.
The results are reported in the journal Nature.