The idea that people can get so cross they give themselves a heart attack could be true - at least in people who already have a heart problem. Previous studies have linked wars, earthquakes and even the World Cup to temporary increases in heart attacks. Researchers at Yale University studied 62 people who had heart disease and who had been fitted with an implantable defibrillator which gives an electric shock to correct dangerously irregular heart rhythyms. They were asked to remember a recent incident which had made them angry and the electrical instability in their heart was measured. The researchers found that anger did increase this electrical instability. The participants were followed over the next three years and those who had shown the greatest electrical instability in response to anger were 10 times more likely to have an irregular heartbeat. It is unclear whether anger has similar damaging effects in people with healthy hearts.