Some heart attacks have no symptoms, but it does not mean that they are not deadly.

A new study revealed that "silent heart attacks" (SHA) make up nearly half of all heart attacks, and those who have had them do not even know they have had it.

SHA is defined as the Electrocardiogram (ECG)-based evidence of heart attacks without clinical documentation of the person.

The study, published in the American Heart Association's publication Circulation, involved analyzing the records of 9,489 participants who were already taking part in a heart disease risk study.

Cross examination revealed that over the years, there had been 317 people who have had SHA and 386 have had a normal heart attack.

The study also revealed that although SHA is common in males, it is deadlier in women.

Below are other significant findings about SHA:

  1. SHA does the same damage as a normal heart attack. 
  2. SHA increased the chances of dying from coronary heart disease three times.
  3. SHA increased the incidence of death from any cause by 34 percent.

Because SHA has mild symptoms, they often go unnoticed, but Elsayed Z. Soliman, M.D., MSc., M.S., study senior author and director of the epidemiological cardiology research center at Wake Forest Baptist Medical Center, Winston-Salem, North Carolina said it is not something that should be ignored and it should be treated as assertively as heart attacks that go noticed.

"The modifiable risk factors are the same for both kinds of heart attacks," he told Eurekalert journal.

"Doctors need to help patients who have had a silent heart attack quit smoking, reduce their weight, control cholesterol and blood pressure and get more exercise," he added.

According to, the best way to identify if you have already had them is by going to the doctor and undergoing ECG (electrocardiogram; measures heart activity) and testing blood for cardiac enzymes.

SAH can happen to anyone, but people most likely affected are those who had previously had them, those with diabetes and people who are over the age of 65.