Interestingly, despite a greater risk among men, it was women most likely to die of a silent heart attack, at least in this study analysis.
For many users, the silent heart attack is accompanied by symptoms that are so mild most patients barely notice them.
"The outcome of a silent heart attack is as bad as a heart attack that is recognised while it is happening", says Dr. Elsayed Z. Soliman, study senior author and director of the epidemiological cardiology research centre at Wake Forest Baptist Medical Centre, Winston-Salem in North Carolina.
However, "because patients don't know they have had a silent heart attack, they may not receive the treatment they need to prevent another one", Soliman said in a statement.
Even without the traditional symptoms, blood flowing to the heart is reduced or choked off completely during a silent cardio infarction. The heart's electrical activity is altered, even years after a silent heart attack, according to the study.
Soliman said that silent heart attacks, once discovered, should be treated as aggressively as heart attacks with symptoms. It analyses the causes and outcomes of atherosclerosis - which is the hardening of the arteries - over time in the study participants who were free of heart disease at the start of the study.
While the study wasn't created to look at why these differences between men and women may exist, scientists know that men and women experience heart disease in different ways, Soliman said.
Like heart attacks with symptoms, silent heart attacks increase the risk of death.
Earlier studies on the incidence of silent heart attacks had thrown up varying figures: anything from 22 per cent to 60 per cent of all heart attacks.
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said: 'This study emphasises that individuals who have ECG (scan) results which suggest a heart attack, but who don't have any classical symptoms, should be investigated more fully to determine their need for future treatment.
Every 43 seconds, an American has a heart attack.
In 1987, the ARIC Study began enrolling participants who were free of heart disease in four US communities in Maryland, Minnesota, Mississippi and North Carolina to determine the risk factors for heart disease and health effects of hardening of the arteries over time. "I mean, if you lose heart muscle, you've got scar tissue, you've got weakening of the heart muscle", he said.
The researchers analysed the records of 9,498 middle-aged adults already enrolled in the Atherosclerosis Risk in Communities, a study conducted in four U.S. communities that began in 1987.
Half the participants were followed for more than 13 years.
The researchers accounted for factors such as smoking, weight, diabetes, high blood pressure, and cholesterol. They did not adjust for access to care but did adjust for income and education, which could impact access to care.
Dr. Freeman is one of the spokespersons for the American College of Cardiology.
"In a country where the diet and exercise patterns are not ideal, there may be a lot of folks we may never come in contact with who may have this problem", he said.
Soliman and his colleagues published their findings today in the research journal Circulation. On the flip side, whites had a higher rate of clinical heart attack than blacks.