Suffering longer-term stress and then experiencing a stressful event - such as the loss of a loved one - could trigger a condition known as takotsubo syndrome, also known as broken heart syndrome.

Symptoms of the condition often mimic a heart attack and include chest pain and shortness of breath.

It can cause a range of complications and affects around 2500 people in the UK each year, mainly post-menopausal women. In some cases, it is fatal.

Broken heart syndrome often follows an intense event, such as the death of a loved one, a life-threatening medical diagnosis, losing a lot of money, redundancy or a relationship breakdown.

New research funded by the British Heart Foundation (BHF) and published in the journal Cardiovascular Research has found two molecules linked to increased stress levels play a key role in the development of the syndrome.

Experts from Imperial College London found that increased levels of microRNAs -16 and -26a - small molecules that regulate how genes are decoded - increase the chance of suffering the syndrome.

Researchers examined human and rat heart cells and measured how they responded to adrenalin after exposure to the two molecules.

They found cells treated with microRNAs were more sensitive to adrenalin and more likely to develop loss of contraction.

Changes linked to broken heart syndrome were therefore seen at lower levels of adrenalin.

The microRNAs in question are linked to depression, anxiety and increased stress levels, suggesting longer-term stress followed by a dramatic shock could trigger the effects seen in broken heart syndrome.

Experts hope a blood test or drugs may now be developed in response to the findings.

"Takotsubo syndrome is a serious condition, but until now the way it occurs has remained a mystery," Sian Harding, professor of cardiac pharmacology at Imperial College London, said.

"We don't understand why some people respond in this way to a sudden emotional shock while many do not.

"Stress comes in many forms and we need further research to understand these chronic stress processes."

Professor Metin Avkiran, associate medical director at the British Heart Foundation, said: "Takotsubo syndrome is a sudden and potentially catastrophic heart problem but our knowledge about what causes it remains limited.

"As such, it is vital that we learn more ... and develop new ways of preventing and treating it."

Australian Associated Press