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Most people don’t know that you can have a heart attack without realizing it. In fact, these so-called silent heart attacks account for an estimated 30% to 60% of all heart attacks.

Recognizing and responding to a silent heart attack is important, as it can be a harbinger of a more serious, potentially deadly heart attack.

“Heart attacks can be silent for a variety of reasons,” said cardiologist Dr. Peter Stone, professor of medicine at Harvard Medical School. Just like a regular heart attack, a silent one occurs when the heart muscle doesn’t receive enough blood — usually when a clot blocks blood flow inside a narrowed heart artery.

The quality, duration and intensity of the resulting pain can vary quite a bit. Some people describe the sensation as a dull ache or crushing pressure, which may be mild or short-lived and, therefore, unnoticed or ignored.

Typically, the reduced blood flow must last about 15 to 30 minutes to result in a detectable heart attack (that is, part of the heart muscle becomes damaged or dies).

Sometimes, symptoms come and go, which doctors refer to as stuttering symptoms. “When a clot obstructs an artery, the body’s natural clot-busting process is instantly set in motion,” Stone explained. If the clot dissolves, symptoms may abate — but then return if the clot-forming forces win.

Radiating and referred pain

Various quirks related to pain perception may also play a role in a heart attack going unrecognized.

“People often think the discomfort has to be on the left side of the chest because that’s where the heart is located,” Stone said. But nerves within the heart can send signals to the surrounding nerves, causing pain that may radiate to the stomach, back, neck, arm or jaw.

For example, if an artery blockage occurs near the bottom of the heart, it may affect nerves in the diaphragm — the muscular membrane that separates the chest from the abdominal cavity. This can be perceived as abdominal discomfort or nausea.

Or people may experience shoulder pain, a classic example of referred pain. This phenomenon — when pain is felt in a location other than the actual source — happens because of overlaps in the network of nerves in the spinal cord.

Mistaken attributions

Problems with the lungs and the esophagus are sometimes mistaken for a heart attack, but the opposite can also occur.

Sometimes, people assume their chest pain is caused by a respiratory infection or other lung disease when they’re actually having a heart attack.

Another possible misattribution is heartburn, which happens when stomach acid rises up into the esophagus. [See “Ways to overcome heartburn discomfort” on page 8.]

If you have diabetes, you’re more likely to have a silent heart attack. Over time, high blood sugar can damage your nerves and the small blood vessels supplying those nerves — including those that transmit pain signals.

While pain tolerance may be physiological, emotional and cultural factors can come into play as well, said Dr. Stone. For instance, people may dismiss or ignore pain because they don’t want to appear weak.

Diagnosing a silent heart attack

Heart muscle damage from a heart attack creates a distinct signature on an electrocardiogram (ECG), a recording of the heart’s electrical activity. A heart ultrasound (echocardiogram) can also detect a prior heart attack. If either test suggests heart damage, it should be a wake-up call to prioritize efforts to avoid more damage.

Follow healthy lifestyle habits (and take medications, if necessary) to make sure your weight, blood pressure, cholesterol and blood sugar are within normal ranges.

© 2023 by Harvard University

Varied heart attack symptoms

During a heart attack, about three-quarters of both men and women experience the classic symptom of chest discomfort that spreads through the upper body.

But some people experience other symptoms. These less-common symptoms might be slightly more frequent in women and in older people, but they can also happen in men and younger people.

Classic symptoms:

• Pressure, aching or tightness in the center of the chest
• Pain or discomfort that radiates to the upper body, especially shoulders or neck and arms
• Sweating

Other symptoms:

• Shortness of breath
• Weakness
• Nausea or vomiting
• Dizziness
• Back or jaw pain
• Unexplained fatigue