Heart disease is a major killer in the UK
Nearly four million people in the UK may be unaware they are at high risk of heart disease, research suggests.
One in three of those most at risk over the next 10 years remain undiagnosed, the study estimates.
An University of Oxford team screened more than 71,000 people aged over 18 across England, Wales and Scotland.
Campaigners warned the study, published in the International Journal of Clinical Practice, showed too many people took their health for granted.
Plans are in place in England to screen everybody between the ages of 40 and 74 for cardiovascular disease. Scotland has so far not followed suit.
The Oxford study suggests that 7.9 million people in the UK have been diagnosed with cardiovascular disease, or are known to be at risk of developing symptoms.
But it estimates that a further 2.8 million men and 900,000 women at high risk have not been diagnosed.
The problem is particularly severe among middle aged men, the study suggests.
Lead researcher Professor Andrew Neil, said: "Our findings reinforce the need for a national cardiovascular disease risk assessment programme."
The study found 75% of men and 45% of women who were over 50 already had cardiovascular disease or diabetes, were taking cholesterol or blood pressure drugs or were at high risk of developing cardiovascular disease.
Barbara Harpham, national director of Heart Research UK, said: "The stark reality, shown by this report, is that people take the health of their heart for granted and it is not high on their agenda to check it is OK.
"Ask anyone, particularly women, what they are most likely to die of and they will probably say cancer.
"In fact, it is cardiovascular disease, mostly due to our unhealthy lifestyles."
The Oxford study concludes that wider access to cholesterol-lowering statins is the only policy that is likely to reduce the burden of cardiovascular disease in the short term.
It says more effective national nutritional policies and lifestyle measures would have a longer-term impact.
The report also warns that it is unclear whether uptake of screening in deprived areas will be high enough to reduce widening health inequalities.