Ana Baylin and colleagues at the Brown University School of Medicine in Providence, Rhode Island, studied 503 cases of non-fatal heart attacks in Costa Rica. They surveyed participants about their coffee consumption in the hours and days before their heart attack and also studied their lifestyle and medical history.

The researchers found that for people with multiple risk factors for a heart attack and those who have a sedentary lifestyle, a cup of coffee could be the final straw, reported the online edition of health magazine WebMD.

The researchers suggest that caffeine causes short-term increase in blood pressure and sympathetic nervous activity that could trigger a heart attack. "It can trigger a heart attack within an hour in some people," said Baylin.

They said moderate coffee drinkers (those who consumed two-three cups a day) raised their risk of having a heart attack by 60 per cent.

Light drinkers increased their risk of heart attack by more than four times with one cup, the study observed. Little effect was seen among heavy coffee drinkers (those who drank four or more cups per day).

Further, coffee drinkers who have three or more risk factors for heart disease more than doubled their risk of sustaining a heart attack after downing a cup.

Although the study was conducted in Costa Rica, the researchers say the results are relevant to people who have similar caffeine habits.