Do you work for long hours? Beware as it may increase the risk of developing an irregular heart rhythm - known as atrial fibrillation - as well as contribute to the development of stroke and heart failure, according to a study. The findings showed that, compared to people who worked a normal week of between 35-40 hours, those who worked 55 hours or more were approximately 40 percent more likely to develop atrial fibrillation. "A 40 percent increased extra risk is an important hazard for people who already have a high overall risk of cardiovascular disease due to other risk factors such as older age, male sex, diabetes, high blood pressure, high cholesterol, overweight, smoking and physical inactivity or living with an established cardiovascular disease," said Mika Kivimaki, Professor at the University College London. Also Watch: "This could be one of the mechanisms that explain the previously observed increased risk of stroke among those working long hours. 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," Kivimaki added. For the study, published in the European Heart Journal, the team 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. During the ten-year follow-up period, there were 1,061 new cases of atrial fibrillation.This gave an incidence rate of 12.4 per 1,000 people in the study, but among the 4,484 people working 55 hours or more, the incidence was 17.6 per 1,000.