Before starting the study, researchers came to a theory that caffeine causes short-term increases in blood pressure and sympathetic nervous activity that could affect a atherosclerotic plaque and trigger a heart attack within an hour of consumption.
503 cases of non-fatal myocardial infarction were asked about their coffee consumption in the hours and days before their heart attack. The study results showed them that those people who were light or occasional coffee drinkers, especially those who had a sedentary lifestyle were at the highest risk of suffering a heart-attack. Moderate coffee drinkers increased their chances of suffering a heart-attack by 60 percent after having just one cup of coffee. However, light coffee drinkers increased their chances four times. Interestingly, heavy coffee drinkers had no increased risk of suffering a heart attack.
It is thought that this is because the heavy drinkers were acclimated to the caffeine while the others were not.
Researchers suggest that those people who are at high risk of a heart attack should be better of without coffee altogether.