Scientists believe they have found some vital clues to how stress can trigger a heart attack in vulnerable patients.
It is known stress causes heart attacks but not exactly how
UK researchers focused on men who had suffered a heart attack or acute chest pain triggered by stress.
They found evidence that stress can elevate blood pressure over an extended period, and trigger the release of high levels of clot-forming platelets.
The University College London (UCL) study is published in Proceedings of the National Academy of Sciences.
The UCL team looked at 34 men who had suffered a heart attack or severe chest pain an average of 15 months earlier.
From these they identified 14 whose symptoms had been preceded by acute stress, anger and depression.
The volunteers were given a series of stressful tasks to do, including imagining stressful situations and making a speech.
Measurements were then taken of their blood pressure and chemistry.
In all men the blood pressure, heart rate and cardiac output increased in response to the induced stress.
But in the group identified as particularly vulnerable to stress blood pressure took longer to return to normal levels.
This group also recorded higher levels of platelets - the small blood cells that form clots to stop bleeding - in their blood.
Lead researcher and Professor of Psychology for the BHF Andrew Steptoe said: "What's been suspected for a number of years is that emotional stress can trigger heart attack in people who are vulnerable.
"What this study does is to provide some information about the biology underpinning that response and why it is that certain people may be vulnerable.
"It is something to do with the way particular people react to emotional stress."
He said the finding of high platelet levels was key.
Platelets clump together to stop bleeding when a tear occurs in the vessel wall during a heart attack.
However, they in turn can cause a blockage in the heart which prevents the blood from flowing in the heart.
Alison Shaw, a spokeswoman for the British Heart Foundation which funded the study, said it provided vital clues into the biological reasons why stress can trigger heart attacks.
"Currently, we can't easily tell whose bodies respond poorly to stressful events, but we can all help ourselves by recognising what stresses us out and coming up with coping strategies to help control how we respond to these situations."
Dr Nick Brooks, president of the British Cardiac Society and consultant cardiologist at South Manchester University Hospital NHS Trust, said the study was ingenious but limited by the small numbers involved.
He said it showed that people with similar perceived levels of stress responded in different ways.
"For those in whom stress provokes these major changes - they seem to be at a greater risk of a coronary," he added.