The vast majority of people have an older "heart age" than their actual age, a new study suggests.
An online test which calculates a person's risk of having a heart attack or stroke reveals that almost four in five people over the age of 30 have a heart which is deemed to be older than their chronological age.
This means they are at a higher risk of potentially fatal heart attack or stroke.
The new study, published in the journal BMJ Open, examined data from 575,000 people who used the online tool on the NHS Choices website.
Two-fifths of women under 40 had a heart older than they actually were compared to 87% of men the same age, according to the research, funded by the British Heart Foundation (BHF).
It also found that many people were unaware about their own cardiovascular risk factors - almost half did not know their blood pressure and three-quarters were unaware what their cholesterol levels were.
Those who used the online tool who do not know their blood pressure or cholesterol levels can still be given an estimate for their "heart age", but they are encouraged to find out their measurements.
Public Health England, the BHF and NHS Choices are encouraging people to use the tool to check their "heart age" and find out their cardiovascular risk.
"Even though you may not have symptoms, having a heart age higher than your own age indicates an increased risk of serious illness," said Jamie Waterall, national lead for cardiovascular disease prevention at Public Health England.
"The Heart Age Tool gives an immediate indication of a person's potential risk and what they can start doing to reduce it.
"For people over 40, the NHS Health Check presents an invaluable opportunity to discuss your heart health with a professional."
Dr Mike Knapton, BHF associate medical director, added: "Knowing your heart age is vital to taking control of your health.
"Armed with this knowledge you can start to make changes to help protect yourself against cruel and life-changing events such as heart attack and stroke.
"The younger you start making small but significant changes, the greater the return on your investment in your health.
"Research has shown that high blood pressure, high cholesterol, smoking, poor diet and a lack of exercise, as well as a lack of investing in your future health and fitness all contribute to increasing your risk of developing cardiovascular disease.
"Why not take action this World Heart Day and make the first steps to improve the health of your heart by logging on and using this simple and quick heart age online tool?"
Cardiovascular disease causes more than a quarter of all deaths in the UK - around 155,000 people each year.
:: People can find out their "heart age" by visiting bhf.org.uk/heartage or the NHS Health Check website.