A heart attack happens when blood flow to part of the heart muscle gets blocked, usually by a blood clot that forms inside a coronary artery. Without blood delivering oxygen, heart cells begin to die. In the United States, someone has a heart attack every 40 seconds, totaling about 805,000 cases per year.
What Happens Inside the Artery
The process that leads to most heart attacks starts years or even decades before the event itself. Cholesterol particles, particularly LDL (often called “bad” cholesterol), gradually build up inside the walls of your coronary arteries. Over time, these deposits form fatty patches called plaques. An LDL level below 100 mg/dL is considered optimal, while levels of 160 mg/dL or higher significantly raise your risk. But the buildup process is silent. You won’t feel it happening.
As plaque grows, it develops a thin fibrous cap on its surface, like a skin holding everything in place. Some plaques stay stable for years. Others become vulnerable: the cap thins out, the core fills with dead cells and fat, and the plaque becomes a ticking clock. These fragile plaques, called thin-cap fibroatheromas, are the ones most likely to rupture.
Rupture can be triggered by a spike in blood pressure, a surge of adrenaline, intense physical exertion, or severe emotional stress. When the cap tears open, it exposes the plaque’s inner material to the bloodstream. Your body treats this like an open wound and rushes to form a clot. That clot can partially or completely block the artery within minutes.
How Heart Muscle Dies
Your heart is a muscle, and like every muscle, it needs a constant supply of oxygen-rich blood. Two main coronary arteries handle the job. The left main coronary artery feeds the left side of the heart, which does the heavy lifting of pumping blood to your entire body. It branches into the left anterior descending artery, supplying the front and middle of the heart, and the circumflex artery, which wraps around to feed the outer side and back. The right coronary artery supplies the right side of the heart and the electrical nodes that control your heartbeat.
When a clot blocks one of these arteries, the region it feeds starts running out of oxygen almost immediately. If blood flow is restored within roughly the first hour, the damage can sometimes be completely prevented. This is called an aborted heart attack, meaning no permanent tissue death occurs. After that window closes, heart cells begin dying in a wave that spreads outward from the center of the affected zone. The longer the blockage lasts, the more muscle is lost, and dead heart muscle does not regenerate. It’s replaced by scar tissue that can’t contract.
Which artery is blocked determines where the damage lands and how severe the consequences are. A blockage in the left anterior descending artery, sometimes called “the widowmaker,” can damage a large portion of the heart’s main pumping chamber. A blockage in the right coronary artery can disrupt the heart’s electrical system, potentially causing dangerous rhythm problems.
Complete vs. Partial Blockage
Not all heart attacks are the same. Doctors distinguish between two main types based on how much of the artery is blocked.
A STEMI (ST-elevation myocardial infarction) occurs when a coronary artery is completely blocked. This is the more dangerous type. It shows a distinct pattern on an ECG, a test that reads the heart’s electrical activity, and it causes widespread damage fast. Treatment typically involves opening the artery as quickly as possible.
An NSTEMI (non-ST-elevation myocardial infarction) happens when the artery is only partially blocked. Blood flow is reduced but not entirely cut off. The ECG won’t show the same dramatic changes, but blood tests will reveal elevated troponin, a protein that leaks from damaged heart cells. NSTEMIs still cause real harm, but the damage tends to be less extensive because some blood continues reaching the muscle.
In both cases, the clot forming on a ruptured plaque is the underlying mechanism. The difference is whether that clot seals the artery shut or leaves a narrow opening.
What It Feels Like
The classic heart attack symptom is chest pain or pressure, often described as a heavy weight sitting on the chest. It can radiate to the left arm, jaw, neck, or back. But this textbook presentation is more common in men than in women.
Women frequently experience symptoms that don’t match the stereotype. Sweating, nausea, dizziness, and unusual fatigue are common, and these symptoms may appear while resting or even during sleep. Shortness of breath, vomiting, pain in the upper abdomen, and extreme fatigue are all reported. The chest discomfort, when present, is often not the most prominent symptom. This mismatch with the “classic” picture is one reason women are more likely to delay seeking help.
About 1 in 5 heart attacks are silent. The damage happens, but the person doesn’t recognize it at the time. These are often discovered later during routine testing and are particularly common in people with diabetes, whose nerve damage can blunt pain signals.
What Happens in the First Minutes
Speed is everything during a heart attack. The single most important action is calling emergency services immediately. While waiting, the American Heart Association recommends that a conscious adult experiencing chest pain chew and swallow 162 to 325 milligrams of aspirin (roughly one to two regular tablets), unless they’re allergic or have been told not to take it. Chewing gets the aspirin into the bloodstream faster than swallowing it whole, and it helps slow clot growth in the blocked artery.
At the hospital, doctors use an ECG and blood tests measuring troponin levels to confirm whether a heart attack is occurring and what type it is. Troponin above a certain threshold, specific to your age and sex, signals that heart cells have been damaged. From there, treatment focuses on restoring blood flow as fast as possible.
Recovery and Reducing Your Risk of a Second Event
Of the 805,000 heart attacks that occur in the U.S. each year, about 200,000 happen to people who have already had one. A first heart attack significantly raises the odds of a second, which makes recovery and lifestyle changes critical.
Cardiac rehabilitation is the standard path after a heart attack. Most insurance plans, including Medicare, cover a program of 36 supervised sessions over 12 weeks. These programs combine exercise training, education on heart-healthy habits, and stress management counseling. The goal is to rebuild physical fitness, lower blood pressure and cholesterol, and help you return to daily activities with confidence.
The modifiable risk factors are well established: high LDL cholesterol, high blood pressure, smoking, physical inactivity, obesity, and poorly managed diabetes. Bringing LDL below 100 mg/dL (or lower for those who already have artery disease) is a key target. Regular physical activity, a diet low in saturated fat, maintaining a healthy weight, and not smoking all reduce the chance that another plaque will rupture and another clot will form.