A heart attack happens when blood flow to part of your heart muscle gets blocked, usually by a blood clot that forms inside a coronary artery. Without blood supply, heart cells start dying within minutes. About one in four heart attacks produces so few symptoms that the person doesn’t realize it happened until a doctor finds evidence on a later test.
What Happens Inside Your Arteries
The process starts years before the actual event. Fatty deposits slowly build up inside the walls of your coronary arteries, the vessels that feed oxygen-rich blood to your heart muscle. These deposits, called plaques, are made of cholesterol, calcium, and inflammatory cells. A plaque can sit quietly for decades, gradually narrowing the artery without causing problems.
The critical moment comes when a plaque breaks open. This tends to happen at the thinnest, weakest point of the plaque’s outer shell. In autopsy studies, ruptured caps averaged just 23 micrometers thick, roughly a quarter the width of a human hair. When that shell cracks, the fatty interior of the plaque is suddenly exposed to your bloodstream. Your body treats this the same way it treats a cut on your skin: it sends clotting factors to seal the wound. A blood clot forms right there inside the artery.
If that clot grows large enough, it blocks the artery entirely. Blood can no longer reach the section of heart muscle downstream. Sometimes pieces of the clot or plaque material break off and travel deeper into smaller branches of the artery, plugging those too. Either way, heart cells that depend on that blood supply are now starving for oxygen.
How Quickly Heart Muscle Dies
The timeline is tight. Within the first 20 minutes of lost blood flow, heart cells swell and lose their ability to contract, but they can still recover if flow is restored. Once ischemia passes the 20-minute mark, cells begin dying permanently. By 60 minutes, most cells in the affected area are irreversibly damaged.
This is why speed matters so much during a heart attack. Every minute that passes without treatment means more muscle tissue lost. The heart can’t regenerate those cells. Whatever area dies is replaced by scar tissue, which doesn’t pump. The larger the area affected, the weaker the heart becomes afterward.
What a Heart Attack Feels Like
The most common symptom is chest pain or discomfort, often described as pressure, tightness, squeezing, or a heavy aching sensation. It’s not always sharp or stabbing. Many people say it feels like someone is sitting on their chest. The pain frequently spreads to the left shoulder, arm, back, neck, jaw, teeth, or upper abdomen.
Beyond chest pain, you may experience:
- Shortness of breath
- Cold sweat
- Nausea or what feels like heartburn
- Lightheadedness or loss of consciousness
- Sudden, unusual fatigue
These symptoms can come on suddenly or build gradually over minutes to hours. Some people notice mild warning signs days before, like unusual tiredness or intermittent chest discomfort with exertion.
Why Symptoms Differ in Women
Women experience chest pain during heart attacks, but they’re more likely than men to have symptoms that don’t seem heart-related at all. Brief neck or back pain, nausea, shortness of breath, and overwhelming fatigue can be the primary signs. Some women have a heart attack with no chest pain whatsoever. Women are also more likely than men to have a heart attack without a severely blocked artery, which can make the event harder to diagnose quickly.
Older adults and people with diabetes also tend toward these less obvious presentations. Diabetes can damage the nerves that transmit pain signals from the heart, which is one reason silent heart attacks are more common in people with the condition. Studies of diabetic patients found that silent events accounted for up to one third of all heart attacks identified.
Silent Heart Attacks
Not every heart attack announces itself. The Framingham Heart Study, one of the longest-running cardiovascular research projects, found that nearly one quarter of all heart attacks over a 20-year follow-up period were “silent,” meaning the person either had no symptoms or symptoms so mild they were dismissed as something else. These events carry a prognosis similar to heart attacks that are recognized at the time.
Silent heart attacks are typically discovered later, when a routine electrocardiogram (ECG) picks up telltale changes in the heart’s electrical pattern, specifically abnormal Q waves that indicate old muscle damage. If those changes show up unexpectedly, doctors usually follow up with cardiac imaging to determine how much tissue was affected.
What Puts You at Risk
The major risk factors fall into two categories: things you can change and things you can’t. Age, sex (men face higher risk earlier in life, though women catch up after menopause), and family history of heart disease are fixed. Everything else is at least partially within your control.
The modifiable risks tracked by the American Heart Association include high blood pressure, high cholesterol, high blood sugar, smoking, physical inactivity, poor diet, obesity, and inadequate sleep. Each of these contributes to the slow buildup of arterial plaque or increases the likelihood that an existing plaque will rupture. Having several of these risk factors at once doesn’t just add up; they compound each other.
What to Do During a Heart Attack
If you think you or someone near you is having a heart attack, call emergency services immediately. Don’t drive yourself to the hospital. Paramedics can begin treatment in the ambulance and alert the hospital to prepare, which saves critical minutes.
While waiting for help, chew an aspirin if the emergency operator recommends it. Aspirin helps slow clot formation, which can limit damage to the heart muscle. Don’t take one before calling for help; the call comes first. If the person becomes unresponsive and stops breathing normally, CPR can keep some blood flowing to the heart and brain until paramedics arrive.
How Doctors Confirm the Diagnosis
At the hospital, doctors use two main tools. An ECG records your heart’s electrical activity and can show patterns that indicate which part of the heart is being damaged and how severely. The second tool is a blood test that measures a protein called troponin, which heart cells release when they’re injured. Levels above the 99th percentile of normal are used to confirm heart muscle damage. Doctors often check troponin levels more than once over several hours, because a rising pattern is more informative than a single reading.
Treatment focuses on reopening the blocked artery as fast as possible. The most common approach involves threading a thin catheter through a blood vessel to the blockage and inflating a small balloon to widen the artery, then placing a stent to hold it open. The goal is to restore blood flow before more muscle dies, which is why hospitals track “door-to-balloon time” as a key performance metric. In cases where this procedure isn’t available quickly enough, clot-dissolving medications can be given through an IV to break up the blockage.
Recovery depends largely on how much heart muscle was lost. Some people return to normal activity within weeks. Others face longer rehabilitation, medication regimens, and lifestyle changes to prevent a second event. About 1 in 5 people who have a heart attack will have another one within five years, making the changes you make afterward just as important as the initial treatment.