Sad and distressing events can trigger a potentially fatal heart condition, but now scientists believe joyous ones can as well.

Hearts can be broken by happy events as well as those causing grief and sadness, a study has found.

Since 1990, doctors have recognised a rare condition associated with extreme emotional distress that can trigger potentially fatal weakening of the heart.

Known as Takotsubo syndrome, or TTS, it typically occurs after upsetting episodes such as the death of a spouse or parent, the breakdown of a relationship, or being diagnosed with cancer.

Now research shows the same outcome can follow happy or joyful events. Scientists have named the new condition "happy heart syndrome".

The discovery came after researchers analysed data from 1750 patients diagnosed with TTS in nine countries.

Of 485 patients for whom an emotional trigger could be identified, 96 per cent had suffered sad and stressful events such as the loss of a loved one, attending a funeral, being hurt in an accident, or experiencing an illness or relationship problems.

But in the case of the remaining 20 individuals, heart damage appeared to have been triggered by happy occasions including a birthday party, wedding, surprise celebration, the birth of a grandchild, or a favourite rugby team winning a game.

Dr Jelena Ghadri, from University Hospital Zurich in Switzerland - where the world's first TTS registry is based - said: "We have shown that the triggers for TTS can be more varied than previously thought. A TTS patient is no longer the classic `broken-hearted' patient, and the disease can be preceded by positive emotions, too.

"Clinicians should be aware of this and also consider that patients who arrive in the emergency department with signs of heart attacks, such as chest pain and breathlessness, but after a happy event or emotion, could be suffering from TTS just as much as a similar patient presenting after a negative emotional event."

Takotsubo syndrome takes its name from a Japanese octopus trap that resembles the distorted shape of the left ventricle of a heart affected by TTS.

The condition, which occurs suddenly, causes the heart chamber to balloon out at the bottom while the neck remains narrow. Patients with the abnormality are prone to chest pains and breathlessness, and at risk of a potentially fatal heart attack.

Scientists are still trying to understand the mechanism behind TTS, which is thought to involve links between psychological stimuli, the brain and the cardiovascular system.

The findings are published in the European Heart Journal.