Health officials have urged adults to check their risk of having a heart attack or stroke using a free online tool.
The Heart Age Test, developed by experts, asks people over the age of 30 to answer a series of questions about their lifestyle and physical health.
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If the tool estimates that an individual's "heart age" is higher than their actual age, they will be told they have an increased chance of having a heart attack or stroke and advised how to cut this risk.
The test has been completed more than 1.9 million times, Public Health England (PHE) said, with four out of five people (78%) recording a heart age higher than their actual age.
More than a third (34%) had a heart age more than five years above their real age and 14% found it was 10 years higher.
Professor Jamie Waterall, national lead for cardiovascular disease at PHE, said: "Millions are at risk of cardiovascular disease but don't know it, putting themselves at real risk of suffering ill-health or dying younger.
"Knowing your heart age is a simple way of finding out whether you're at risk of a heart attack or stroke.
"By making important lifestyle changes you can reduce your risk before it's too late."
Cardiovascular disease is the leading cause of death among men and the second in women.
Around 24,000 of deaths in England every year are in people under the age of 75 and 80% of these are preventable, which is equivalent to around 50 per day, PHE said.
People can improve their heart health by losing weight, quitting smoking, exercising regularly and cutting back on alcohol.
Simon Gillespie, chief executive of the British Heart Foundation, said: "Millions of people in the UK are unknowingly living at high risk of a heart attack or stroke due to their lifestyle, their family history of heart disease, or undiagnosed conditions including high blood pressure and cholesterol.
"Our message today is that it's never too late to change.
"Take the test, and if you are concerned by the age of your heart, make an appointment to see your GP."
The Heart Age Test is available free online at www.nhs.uk/oneyou/hat