People who have a habit of spending long hours at work can be at increased risk of developing heart ailments.
The study showed that, compared to people who worked a normal week of between 35-40 hours, those who worked 55 hours or more were about 40 per cent more likely to develop atrial fibrillation during the following ten years.
For every 1,000 people in the study, an extra 5.2 cases of atrial fibrillation occurred among those working long hours during the ten-year follow-up.
"These findings show that long working hours are associated with an increased risk of atrial fibrillation, the most common cardiac arrhythmia," said Professor Mika Kivimaki, from the University College London (UK), who led the research.
"This could be one of the mechanisms that explain the previously observed increased risk of stroke among those working long hours," said Kivimaki.
"Atrial fibrillation is known to contribute to the development of stroke, but also other adverse health outcomes, such as heart failure and stroke-related dementia," said Kivimaki.
Researchers analysed data from 85,494 men and women from the UK, Denmark, Sweden and Finland who took part in one of eight studies in these countries.
They assessed the participants' working hours when they joined the studies between 1991 and 2004.
Working hours were classified as less than 35 hours a week, 35-40 hours, which was considered as the standard working hours of full-time workers, 41 to 48 hours, 49 to 54 hours, and 55 hours or more a week. None of the participants had atrial fibrillation at the start of the studies.
During the ten-year follow-up period, there were 1,061 new cases of atrial fibrillation.