Symptoms of a heart attack may be subtle and easily overlooked. But that doesn’t mean they are less perilous than a cardiac event that produces pain and pressure. According to recent statistics on heart disease and strokes from the American Heart Association, silent heart attacks account for approximately 20% of all heart attacks. Some cardiologists believe the number is closer to 50%.

“It has been known for a long time that silent heart attacks, identified on an ECG or an echocardiogram ultrasound study, are quite common,” Dr. Joel Kahn, founder of the Kahn Center for Cardiac Longevity in Michigan, tells Newsmax. “Some people can close a heart artery with no symptoms at all or with atypical symptoms of heartburn or shortness of breath that does not prompt them to go to the ER. Nonetheless, silent heart attacks are important and are a reason I check an ECG on all patients I see.”

Heart attacks occur when the arteries that carry blood to the heart become obstructed, and oxygen can’t flow to the heart muscle. This blockage can cause pain or pressure, according to AARP. When a silent heart attack occurs, the same thing happens, says Dr. Eduardo Marban, of the Schmidt Heart Institute at Cedars-Sinai Medical Center in Los Angeles. But the symptoms go unnoticed.

“It’s not necessarily that there were no symptoms,” he says. “It may be that the patient didn’t recognize them as heart symptoms and wasn’t concerned.

Here are some typical, non-classic symptoms of a silent heart attack, according to Harvard Health Publishing, a division of Harvard Medical School:

• Shortness of breath
• Weakness
• Nausea or vomiting
• Dizziness
• Back or Jaw Pain
• Unexplained fatigue

These symptoms may be misdiagnosed even in healthcare settings, Dr. Robert Lager, a cardiologist at MedStar Washington Hospital Center in Washington, D.C., tells AARP, because the signs are often confusing and misleading. However, Lager says that symptoms of heart trouble are “not positional.” This means that the pain in your back does not go away when you stretch or move, and the shortness of breath doesn’t subside when you sit down and take it easy.

“That’s a really good rule of thumb,” says the expert. “If you’re not sure if you’re having a symptom, see if you can manipulate it in some way. Can you press on the chest? Can you change your position? Can you stand up or sit down? Does it make a difference, positionally? Because the heart has no gyroscope; it doesn’t know where it is in space. And it doesn’t matter if you put the heart upside down or right side up, it’s going to give you the same signals if it’s in trouble.”

Lager adds that symptoms will get worse due to the lack of nutrient-rich oxygen in the heart. “So, if someone has chest discomfort at rest and gets up and walks around, you’re increasing the heart’s demand for oxygen, so the symptoms usually will get worse if it’s a heart issue,” he explains.

Marban and Lager emphasize that it is important to be aware of changes in your body, and if symptoms appear out of the blue that are uncommon, have them checked out. If you are prone to indigestion, then that feeling of discomfort in the chest after a spicy meal is likely gastrointestinal, but if it’s something you haven’t experienced before or the symptoms get worse, it may be a sign of a silent heart attack.

Many silent heart attacks are only detected months ― even years ― later. Even though the damage to the heart has already been done, at least your doctor will know how to mitigate health risks in the future.

According to AARP, one study found that having a silent heart attack increases the risk of heart failure by 35%, and other research shows that it also raises the possibility of sudden death, stroke and having another heart attack.