A team from University College London looked at more than 7,000 civil servants over a period of 11 years and established how many hours they worked on an average a day.
They also collected information, including the condition of their heart, from medical records and health checks. Over the period, 192 had suffered a heart attack, reports the journal Annals of Internal Medicine.
The study found that those who worked more than 11 hours a day were 67 percent more likely to have a heart attack than those who had a 'nine to five' job, according to the Daily Mail.
Said Mika Kivimaki, who led the study: 'We have shown that working long days is associated with a remarkable increase in the risk of heart disease.'
The researchers say their findings could potentially prevent thousands of heart attacks a year as they would help physicians get a better idea of how likely a patient was to have one.
Patients already at high risk - by being obese or smoking, for example - could be encouraged to cut down on their working hours.
Around 2.6 million in Britain alone have heart disease, in which the organ's blood supply is blocked by the build-up of fatty deposits in the coronary arteries. It claims 101,000 lives every year in the country.