The effect of constant stress on a deep-lying region of the brain explains the increased risk of heart attack, a study in The Lancet suggests.
In a study of 300 people, those with higher activity in the amygdala were more likely to develop cardiovascular disease – and sooner than others.
Stress could be as important a risk factor as smoking and high blood pressure, the US researchers said.
Heart experts said at-risk patients should be helped to manage stress.
Emotional stress has long been linked with an increased risk of cardiovascular disease (CVD), which affects the heart and blood vessels – but the way this happens has not been properly understood.