Slumping in front of the TV every night after work can double the risk of deadly blood clots, research suggests.
Experts found that sitting down for more than 41 hours a week away from work increases the chance of suffering a blood clot in the lungs.
The study, on almost 70,000 women, found that those who sit for long periods are two to three times more likely to develop a clot than those who sit for less than 10 hours outside of work.
It is thought to be the first study of its kind to find a link between a sedentary lifestyle and pulmonary embolism.
But the researchers, writing in the British Medical Journal, do say the risk is small and is only slightly higher than that for people who fly long haul or women who take the Pill.
A blood clot can travel from deep veins in the legs into the lungs, potentially causing death. Symptoms of a clot include difficulty breathing, chest pain and coughing.
Natasha Stewart, a senior cardiac nurse, said: "We have to be slightly cautious about this research because it only focused on women over the age of 55, but it adds weight to what we already know -- physical activity is great news for your heart and circulation.
"Sometimes, after a long day at work, all we want to do is put our feet up in front of the TV but we know that physical inactivity is linked to heart and circulatory disease.
"Lots of small changes can make a big difference so try getting off the bus one stop earlier or sign up to a new active hobby with your friends.
"Combining at least 30 minutes of physical activity each day with other healthy lifestyle choiceswill also help to protect you from developing circulatory disease conditions."