More than 20 million people in Britain are physically inactive and increasing their risk of heart disease, according to a report by the British Heart Foundation.
The study revealed that the lack of exercise by such a large proportion of the population is costing the NHS around £1.2bn each year.
Inactivity is defined in the report as not reaching the government guidelines for physical activity of 150 minutes of moderate intensity physical activity each week and two days of strength activities.
In the UK alone physical inactivity contributes to almost one in ten premature deaths from coronary heart disease, and one in six deaths from any cause each year.
The charity found different levels of activity in regions throughout the UK with the highest proportion of physically inactive people found to be in the North West of England.
Women are 36% more likely to be classified as physically inactive than men, 11.8 million women compared to 8.3 million men, says the report.
The BHF also estimates the average man spends over a fifth of his lifetime sitting - equivalent to 78 days each year.
In the UK physical inactivity contributes to almost one in ten premature deaths from coronary heart disease, and one in six deaths from any cause.
The organisation say they also found that three quarters of people in England (76%), referred for cardiac rehabilitation after suffering a heart attack or undergoing heart surgery, are considered physically inactive.
This amount rises to as much as 97% in some areas.
Over five million deaths across the world can be attributed to physical inactivity, making it one of the top 10 leading causes of death.
The BHF say being physically active can reduce the risk of heart and circulatory disease by as much as 35% and risk of early death by as much as 30%.