Scientists have made a shocking discovery why being too happy could be catastrophic and deadly for your health.
Too much happiness could trigger a heart attack, a new study has found.
Scientists have long known that extreme emotional distress can cause a potentially fatal weakening of the heart.
But new research has discovered that the same can occur from sheer joy, leading scientists to coin it 'happy heart syndrome'.
Takotsubo syndrome, or TTS, was diagnosed in the 1990s and typically occurs after upsetting episodes such as the death of a spouse or parent, the breakdown of a relationship, or being diagnosed with cancer.
But the new research came after researchers analysed data from 1,750 patients diagnosed with TTS in nine different countries.
Of 485 patients for whom definite emotional trigger could be identified, 96% 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.
One obese patient was stricken after getting stuck in the bath.
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."
The doctor continued: "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.
"Our findings broaden the clinical spectrum of TTS. They also suggest that happy and sad life events may share similar emotional pathways that can ultimately cause TTS."
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.
In the study, 95% of both "broken heart" and "happy heart" patients were women. The average age of the "broken" group was 65 and of the "happy" group 71.
The findings are published in the European Heart Journal.
Co-author Dr Christian Templin, also from University Hospital Zurich, said: "Perhaps both happy and sad life events, while inherently distinct, share final common pathways in the central nervous system output, which ultimately lead to TTS."