On television, a person experiencing a heart attack grasps their chest, gasps for breath, and collapses. But in real life, symptoms of heart attacks are often not that cut and dried.

Up to one-third of heart attacks are “silent” or not accompanied by common symptoms. The heart may sustain damage without ever causing pain–certainly not the “crushing” pain that so often is described as a symptom of heart attack. Hence, many people have heart attacks and do not know that they have had one.

A scary thought since much damage, and even death, can occur without warning.

Researchers say silent or painless heart attacks are more common among women and the elderly. Diabetics are also at higher risk for these kinds of heart attacks.

42-year old Denise Nelson is diabetic but she leads a healthy lifestyle. Since her father suffered heart attacks, and a sister died quietly in her sleep from a heart attack, Nelson has been particularly careful to cut her risks of suffering an MI (myocardial infarction or heart attack). The Arlington, Virginia resident eats well, exercises, and doesn’t smoke or drink. But even this healthy lifestyle could not prevent Nelson from suffering heart problems last year.

Without the family history she may have ignored the “indigestion” she suffered one night after going out for dinner with her parents. But it bothered her, because it was so unusual. “It only lasted a couple of minutes. It wasn’t a tightness in the chest, it wasn’t any tingling in the arms,” Nelson recalls. “There wasn’t any signs whatsoever that would lead me to think that I was having a mild heart attack.”

Still, the fact that she is high risk compelled her to ask her physician for some tests. She eventually learned that three of the arteries into her heart were obstructed. As soon as the diagnosis was made, she was scheduled for triple bypass surgery the next day. The surgeons used a vein from her arm to restore blood flow to her heart.

In retrospect, Nelson can recall one other symptom that may be related to her silent heart attacks. Nelson recalls feeling short of breath at times last summer, but attributed it to the summer heat and poor air quality. Yet neither the shortness of breath nor indigestion prepared her for the fact that she required major heart surgery.

Nelson’s initial reaction to discovering that she had heart problems was anger. “Angry that this could happen to someone that did everything right throughout her whole life,” she explains.

As Nelson learned, doing everything right is not a surefire way to avoid heart problems, and not having classical symptoms of an MI doesn’t mean you haven’t had one either.

“The classic signs of heart attack are chest pain in the middle or the left side of the chest which is severe and crushing in nature,” says Dr. Elizabeth Ross, a cardiologist with the American Heart Association. “It may also be felt in the jaw or shoulder. We usually say that it is associated with shortness of breath, and sweating and sometimes nausea. But patients can have heart attacks with no chest pain at all. And they may just feel short of breath. They may just feel nausea. They may just feel very fatigued.”

These patients may not discover they have suffered heart trouble until they go for a regular physical and their physician does an electrocardiogram, or EKG, that shows the heart’s activity, and notes an abnormality, Ross says. It may also only be diagnosed after a patient has suffered extensive heart damage and complains of other symptoms of heart trouble.

A quick diagnosis that someone has suffered an MI is vital because the more time that goes by after the heart attack, the more heart muscle that is damaged, Ross says. The sooner the patient receives medical attention, the lower the chance that there is permanent damage, she notes.

Of course, the best thing is to avoid having a heart attack at all. Ross says she sees too many people who lead unhealthy lifestyles, putting themselves at risk for heart attack.

“We know smoking is the most important risk factor which will have the most immediate effect in preventing heart attack. If you quit smoking today, your risk of a heart attack is less tomorrow. And within a year is significantly less.”

Ross encourages people to stop smoking, lose weight, start exercising, and eat well. While this will diminish the incidence of heart attacks, there is no way to know if a person will–or has–suffered a silent or painless MI, she says.

“We know that for a lot of people in the United States with heart disease, the first symptom of heart disease is a heart attack.”