The lethal condition 'happy heart syndrome' can occur after a joyful event such as a surprise birthday party or the birth of a child

Celebrating a birthday may not seem like a dangerous pastime but too much happiness can be heartbreaking, according to doctors.

Health experts have known for some time that sad events, such as the loss of a spouse, can trigger a condition known as 'broken heart syndrome' which feels like a heart attack and can be fatal if not treated quickly.

Now for the first time doctors have shown that over-excitement from happy events can also spark the condition, which they have named 'happy heart syndrome.' In short, happiness can be lethal.

Since 'broken heart syndrome' was first identified in 1990, doctors at the University Hospital Zurich in Switzerland have been compiling a database of worldwide attacks which currently holds 1750 patients.

Most attacks were triggered by episodes of severe emotional distress, such as grief, fear and anger. Attending funerals was a common factor and one incident occurred after an obese patient got stuck in the bath.

But for 20 people the condition was precipitated by happy and joyful events, such as a birthday party, wedding, surprise farewell celebration, a favourite rugby team winning a game, or the birth of a grandchild.

Study author Dr Jelena Ghadri, resident cardiologist from University Hospital Zurich said doctors should enquire about happy events as well as sad, when diagnosing heart problems.

"We have shown that the triggers for 'broken heart sydrome' can be more varied than previously thought," she said.