Working long hours may significantly increase your risk of developing heart disease, according to a new study.

Researchers said a long-term study showed that working more than 11 hours a day increased the risk of heart disease by 67 percent, compared with working a standard 7 to 8 hours a day.

They said the findings suggest that information on working hours -- used alongside other factors like blood pressure, diabetes and smoking habits -- could help doctors work out a patient's risk of heart disease.

The researchers studied 7.095 adults aged 39 to 62 years. The participants were free of heart disease and chest pain at the beginning of the study.

Information was collected on heart disease risk factors, including age, blood pressure, cholesterol levels, smoking habits and diabetes. The participants were followed up 11 years later.

Professor Stephen Holgate of the Medical Research Council, which part-funded the investigation, said: "This study might make us think twice about the old adage 'hard work won't kill you'.

"Tackling lifestyles that are detrimental to health is a key area for the MRC, and this research reminds us that it's not just diet and exercise we need to think about."

Experts suspect a number of underlying factors may be at play, such as undetected high blood pressure, stress, anxiety or depression, and being a driven, aggressive or irritable personality.