Hearing shocking news, such as learning of the death of a loved one, really can break your heart, US researchers say.
Hearing unexpected sad news is linked to the release of hormones
A team from Johns Hopkins University suggests patients can suffer days-long surges in adrenalin and other stress hormones which "stun" the heart.
The study, published in the New England Journal of Medicine, says such symptoms can be mistaken for a heart attack.
But these broken hearts can be mended - the damage caused by stress is temporary, usually lasting just weeks.
The researchers examined 19 patients who came into hospital with symptoms similar to those of a heart attack - chest pains, fluid in the lungs, shortness of breath and heart failure.
But when these patients, who were predominantly older women, were examined, it was found that they had no blockages in the arteries supplying the heart, or other clinical signs of a heart attack.
And when doctors investigated further, they found that the patients had very high levels of stress hormones, particularly adrenalin and noradrenalin, in their blood.
The levels seen in these patients were between seven and 34 times those seen in a group of seven heart-attack patients studied.
These stress hormones can be toxic to the heart, say the researchers, effectively stunning it.
The stressed patients also had higher than normal levels of a heart-hormone called brain natriuretic peptide, which indicates the heart is working harder than it normally should.
In addition, echocardiograms - a test which measures heart function, and electrocardiograms, which measure electrical activity in the heart, showed a unique pattern, distinct from the results seen after heart attacks.
All of the 19 had all experienced a severe emotional shock just a few hours before the onset of their symptoms.
Around half had learnt of the death of a partner or relative. Other triggers were being the victim of an armed robbery, speaking in public and facing a court appearance - as well as surprise parties.
But the stressed patients showed "dramatic improvement", and had completely recovered within two weeks.
Magnetic resonance imaging (MRI) scans confirmed that none of the stressed patients had suffered irreversible muscle damage.
In heart attack patients, partial recovery can take weeks or months, and the heart muscle is frequently permanently damaged.
Ilan Wittstein, who led the study, said: "After observing several cases of 'broken heart' syndrome at Hopkins hospitals - most of them in middle-aged or elderly women - we realised that these patients had clinical features quite different from typical cases of heart attack, and that something very different was happening.
"These cases were, initially, difficult to explain because most of the patients were previously healthy and had few risk factors for heart disease."
He added: "Our study should help physicians distinguish between stress cardiomyopathy and heart attacks.
"And it should also reassure patients that they have not had permanent heart damage."
The researchers say it is unclear exactly how stress hormones affect the heart.
But they suggest it could be that the chemicals cause the coronary arteries to spasm, that they have a direct toxic effect on the heart muscle, or that they cause a calcium overload which temporary affects the heart.
The team plan to carry out further research to see if some people are genetically vulnerable to the condition and why it predominantly strikes older women.
Professor Jeremy Pearson, Associate Medical Director of the British Heart Foundation, said: "The researchers have shed some new light and good news on a condition that is known to particularly affect older women - the sudden onset of what appears to be a classic heart attack following severe emotional stress.
"The mechanisms are apparently quite different from other heart attacks, probably due to direct effects of stress hormones on the beating heart cells, and the good news is that unlike most heart attacks the patients generally make a complete recovery without any permanent damage to the heart."