Screening relatives of middle-aged heart attack sufferers would save lives, say experts.
One in five heart attacks occur in middle-aged patients
Siblings and children of younger heart attack victims have a high risk of heart disease but are not routinely assessed, say researchers from Glasgow.
But identifying and treating key signs such as high blood pressure and cholesterol in family members could prevent 42% of premature heart attacks.
The research is published in the British Medical Journal.
Previous research has shown that compared with the general population, siblings of people who have a heart attack when still fairly young - under 55 years in men and 65 years in women - have double the risk of developing heart disease themselves.
Children and partners are also at increased risk because of inherited risk or because of lifestyle factors, such as smoking and diet.
Although several sets of guidelines have recommended screening relatives, this is rarely done in practice.
Researchers from the University of Glasgow estimated that the 15,600 patients admitted for heart attack in 2004 in England and Wales had 32,000 siblings.
They calculated that 218 of those would have a heart attack within a year and 1,148 would have a heart attack within five years, but four in 10 of these were preventable.
Individuals' risk is assessed on the basis of lifestyle factors such as diet and smoking as well as weight, blood pressure and cholesterol.
Current recommendations are that anyone with a 20% 10-year risk of having a heart attack or stroke should receive preventive treatment, such as cholesterol-lowering drugs called statins.
Study leader, Professor Jill Pell, said one method would be to assess the whole adult population, but that would be a big undertaking.
"What we're suggesting is you could do that much more efficiently - you would get a much higher hit rate.
"For every 14 people admitted to hospital with a heart attack we could save one more," she said.
The team are now planning a pilot in Glasgow to assess the impact of such a screening programme in a busy city hospital.
Ellen Mason, heart nurse at the British Heart Foundation, said: "A clear system to invite close relatives of people with premature coronary heart disease for screening could play an important part in preventing heart attacks.
"While there are doctors and nurses in hospitals who encourage visiting relatives to go to their GP surgery to have their risk assessed, often this is not considered a high priority and doesn't happen.
She added: "For most people the risk of having a heart attack comes from habits such as smoking, lack of exercise, being overweight and having a diet too high in saturated fats."