During a heart attack, blood flow to part of the heart muscle is suddenly blocked, and the affected tissue begins to die within minutes. The blockage almost always starts with a fatty deposit inside a coronary artery that cracks open, triggering a blood clot that seals off the vessel. Everything that follows, from the chest pain to the long-term scarring, stems from that moment of interrupted blood supply.
How a Blockage Forms in Minutes
Heart attacks don’t begin with a clean, healthy artery. They begin with plaque, a buildup of cholesterol, fat, and inflammatory cells that has been growing inside an artery wall for years or decades. Most of the time, plaque sits quietly. A heart attack happens when the surface of that plaque cracks or tears open.
Once the plaque ruptures, the inner lining of the artery is exposed to the bloodstream in a way it normally wouldn’t be. Your body treats this the same way it treats a cut on your skin: platelets rush to the site and stick to the exposed tissue, binding to collagen fibers in the artery wall. Those platelets release chemical signals that recruit more platelets, and a chain reaction begins. The blood’s clotting system kicks in alongside, generating a protein mesh that reinforces the growing clot. Within minutes, what started as a microscopic crack can produce a clot large enough to block the artery entirely.
When the clot seals off the artery, oxygen-rich blood can no longer reach the section of heart muscle downstream. That muscle keeps trying to beat, but without oxygen, its cells shift to less efficient energy production, waste products build up, and the tissue starts to break down. Irreversible cell death can begin in as little as 20 to 40 minutes if blood flow isn’t restored, and the damage spreads outward from the center of the affected zone over the next several hours.
What It Feels Like
The most recognized symptom is chest pain or pressure, often described as a heavy weight sitting on the chest. This sensation can radiate into the left arm, neck, jaw, or back. But a heart attack doesn’t always announce itself this dramatically, and the symptoms vary significantly between men and women.
In women, chest pain is not always the most prominent symptom. Instead, many women experience shortness of breath, nausea or vomiting, back or jaw pain, dizziness, lightheadedness, or extreme fatigue. These symptoms can appear during rest or even during sleep, which makes them easy to dismiss. Because the presentation is often vague, women’s heart attacks are more frequently misinterpreted, both by the person having one and by the people around them.
Men more commonly report the “classic” crushing chest pain, though they can also have atypical symptoms. Cold sweats, sudden nausea, and a feeling of impending doom are common regardless of sex.
Silent Heart Attacks
Roughly 5% to 30% of all nonfatal heart attacks are “silent,” meaning they produce no obvious symptoms or symptoms so mild the person never seeks medical attention. These are typically discovered later, sometimes months or years afterward, when an electrocardiogram (EKG) or imaging scan reveals evidence of old damage. Silent heart attacks carry the same long-term risks as ones you feel, including heart failure and a higher chance of a second event.
Complete vs. Partial Blockage
Not all heart attacks involve the same degree of obstruction, and doctors distinguish between two main types based on what shows up on an EKG.
- STEMI: A complete blockage of a coronary artery. The EKG shows a specific pattern called ST-segment elevation, which signals that a large area of heart muscle is losing blood supply. This is the more dangerous type and requires the fastest possible intervention.
- NSTEMI: A partial blockage or a temporary disruption of blood flow. The EKG changes are subtler or absent, and the damage to the heart muscle is typically less extensive, though it still requires urgent treatment.
Both types are medical emergencies. The distinction matters because it determines how quickly doctors move to physically open the blocked artery.
What Happens at the Hospital
The first thing doctors do is confirm the diagnosis. An EKG can reveal the electrical signature of a heart attack within minutes of arrival. A blood test measures a protein called troponin, which heart muscle cells release when they’re injured. Rising troponin levels, measured against the 99th percentile of the normal range for the specific test being used, confirm that heart tissue is being damaged.
For a STEMI, the goal is to reopen the blocked artery as fast as possible. The benchmark is to have a catheter threaded to the blockage site and a small balloon inflated to restore blood flow within 60 minutes of arrival if paramedics transmitted an EKG on the way in, or within 80 to 90 minutes if no pre-hospital EKG was done. Every minute of delay means more heart muscle lost. During the procedure, doctors typically place a small metal tube called a stent to hold the artery open.
For an NSTEMI, the timeline is slightly less urgent but still measured in hours. Medications to thin the blood and prevent the clot from growing are started immediately, and the decision to open the artery with a catheter is made based on the severity of the situation.
What You Can Do Before Help Arrives
If you suspect a heart attack, call emergency services first. While waiting, chewing and swallowing a full-dose aspirin (325 mg) can help slow the growth of the clot. Chewing is preferred over swallowing whole because it gets the drug into your bloodstream faster. Don’t take aspirin if you’re allergic to it or have been told by a doctor that it’s unsafe for you. The 911 operator can help you decide.
Sitting upright or in whatever position feels most comfortable, staying as calm as possible, and not driving yourself to the hospital are the other key steps. Paramedics can begin treatment in the ambulance and transmit your EKG ahead to the hospital, which shaves critical minutes off the timeline.
Complications in the First Hours and Days
The initial blockage is only the beginning of what can go wrong. As heart muscle dies, the heart’s electrical system can malfunction, triggering abnormal rhythms. Both dangerously fast and dangerously slow heartbeats can occur, typically in the first hours to days after the event. This is one of the main reasons heart attack patients are monitored continuously in a hospital.
About 5% to 10% of people with a heart attack develop cardiogenic shock, a condition where the heart is too damaged to pump enough blood to meet the body’s needs. This is the most life-threatening immediate complication. Around 10% develop inflammation of the sac surrounding the heart (pericarditis), usually within days. In rare cases, the damaged muscle wall can tear, or a valve inside the heart can fail if the muscle supporting it dies.
How the Heart Heals Afterward
Heart muscle cells, unlike skin or bone cells, cannot regenerate. The body replaces dead heart tissue with scar tissue, a process that unfolds over weeks in a predictable sequence.
In the first days, the immune system floods the damaged area with inflammatory cells that clear away dead tissue. This cleanup phase involves one type of immune cell that breaks down debris and another type that arrives later to begin the repair process, activating cells that produce collagen. Over the following weeks, collagen is deposited to form a scar. The scar is structurally tough but cannot contract the way healthy heart muscle does.
This remodeling process doesn’t only affect the area that lost blood supply. The surviving heart muscle has to work harder to compensate, and over time, the heart’s chambers can change shape, stretching or thickening in ways that reduce pumping efficiency. This is called ventricular remodeling, and it’s the main reason why people can develop heart failure months or years after a heart attack, even if the initial event seemed manageable. Medications prescribed after a heart attack are largely aimed at slowing this remodeling and reducing the workload on the surviving muscle.
The size of the scar determines how much pumping capacity is permanently lost. A small heart attack treated quickly may leave minimal damage and little noticeable change in daily life. A large one, especially if treatment was delayed, can reduce heart function enough to cause lasting fatigue, shortness of breath, and exercise intolerance. This is why the speed of treatment matters so much: every minute of restored blood flow means less dead tissue and a smaller scar.