A heart attack happens when blood flow to part of the heart muscle gets blocked, starving that tissue of oxygen until it starts to die. The most common cause is a buildup of fatty plaque inside a coronary artery that suddenly ruptures, triggering a blood clot that seals off the vessel. The damage starts becoming irreversible within about 20 minutes of the blockage, which is why speed matters so much when symptoms appear.
How Plaque Builds Up in Your Arteries
The process that leads to most heart attacks begins years or even decades before the event itself. It starts with damage to the inner lining of a coronary artery, the thin layer of cells that keeps blood flowing smoothly. High blood pressure, smoking, high cholesterol, and high blood sugar can all injure this lining over time.
Once the lining is damaged, cholesterol particles (specifically LDL, the “bad” cholesterol) slip through the wall and lodge in the tissue beneath. The immune system treats this like an injury and sends white blood cells to clean it up, but those cells absorb the cholesterol, swell into foam-like blobs, and get stuck. Over time, this creates a growing mound of fat, dead cells, and debris inside the artery wall, covered by a thin fibrous cap. That mound is a plaque.
Many people live with stable plaques for years without symptoms. The artery narrows gradually, and the body can sometimes compensate by rerouting some blood flow. The real danger isn’t the slow narrowing. It’s what happens when a plaque becomes unstable.
The Moment a Plaque Ruptures
Inside an unstable plaque, immune cells release enzymes that chew away at the fibrous cap holding everything together. The cap thins, weakens, and eventually tears open. When it does, the fatty, cholesterol-rich core of the plaque is suddenly exposed to the bloodstream.
Your blood treats this exposed material the same way it treats any open wound: it starts clotting. Platelets rush to the site, stick to the damaged surface, and release chemical signals that recruit more platelets. A protein called tissue factor, which is the most clot-triggering substance inside plaques, accelerates the process. Within minutes, a blood clot can form large enough to partially or completely block the artery.
What happens next depends on the size of the clot and whether your body can dissolve it. In some cases, the clot grows until it completely seals the artery, cutting off all blood flow downstream. In others, pieces of the clot break off and travel further into smaller branches, blocking flow there instead. Sometimes the body dissolves the clot quickly enough that the damage is minimal, and the plaque heals over with scar tissue, leaving the artery a little narrower than before. That third scenario can happen without you ever knowing it occurred.
Which Arteries Supply the Heart
Your heart muscle is fed by two main coronary arteries, the left and the right, which branch off the aorta just above the heart. Where the blockage occurs determines which part of the heart is damaged and how severe the consequences are.
The left main coronary artery splits into two major branches. The left anterior descending artery runs down the front of the heart and feeds the front wall of the left ventricle, the chamber that pumps blood to your entire body. It also supplies the front two-thirds of the wall separating the left and right ventricles. This is sometimes called the “widow-maker” artery because a blockage here can damage a large portion of the heart’s main pumping chamber. The left circumflex artery wraps around to supply the side and back of the left ventricle.
The right coronary artery feeds the right side of the heart and, in about 90% of people, supplies the electrical nodes that control heart rhythm. A blockage here can cause dangerous rhythm disturbances in addition to muscle damage.
How Quickly Heart Muscle Dies
Once blood flow stops, the affected heart muscle cells begin struggling almost immediately. For roughly the first 15 minutes, the damage is still reversible. If blood flow is restored during this window, the cells can recover.
Between 20 and 60 minutes, cells in the most oxygen-starved zone start dying permanently. The damage spreads outward from the inner layers of the heart wall (closest to the blood-empty chamber) toward the outer surface. The longer the artery stays blocked, the larger the zone of dead tissue becomes. This is why emergency treatment focuses on reopening the artery as fast as possible, and why the phrase “time is muscle” is used in cardiology.
Dead heart muscle cells are eventually replaced by scar tissue, which can contract but not pump. A large area of scarring weakens the heart permanently and can lead to heart failure months or years later.
Heart Attacks Without Plaque Rupture
While plaque rupture causes the majority of heart attacks, it’s not the only mechanism. In spontaneous coronary artery dissection (SCAD), the wall of a coronary artery tears on its own, without any plaque involvement. Blood seeps into the tear and collects between the layers of the artery wall, forming a pocket that compresses the channel from the outside and chokes off flow. SCAD is a leading cause of heart attacks in women under 50 and in people with few traditional risk factors.
Coronary artery spasm is another cause. The muscular wall of an artery can clamp down suddenly and severely enough to stop blood flow, even in an artery with no plaque buildup at all. Cocaine use, extreme cold exposure, and severe emotional stress are known triggers.
What a Heart Attack Feels Like
The classic symptom is chest pain or pressure, often described as a squeezing or heaviness in the center of the chest. Men report chest pain as their primary complaint about 13 to 15% more often than women do. Men also more frequently experience sweating and a burning or pricking pain sensation.
Women tend to present with a wider range of symptoms. Nausea, vomiting, dizziness, shortness of breath, and jaw or neck pain are all more common in women than in men. Women between 18 and 55 report about 10% more total symptoms per heart attack than men of the same age, and that gap widens to 17% in people over 75. Pain in the upper back, left shoulder, left hand, or abdomen is also reported more frequently by women.
Perhaps most important: a significant number of heart attacks produce no obvious symptoms at all. Roughly 30% of heart attacks in women and 16% in men go unrecognized at the time they happen. Overall, somewhere between 20% and 40% of all heart attacks are “silent,” discovered only later when an ECG or imaging study reveals scar tissue on the heart.
What Raises Your Risk
The major risk factors for plaque buildup, and therefore for heart attack, are high blood pressure, high cholesterol, diabetes, smoking, obesity, and a family history of heart disease. The impact of managing even one of these is significant.
Lowering systolic blood pressure by 20 points and diastolic by 10 points cuts the risk of dying from coronary heart disease roughly in half for people aged 40 to 49, and by about a third for people in their 80s. Cholesterol has a similarly powerful effect: a 10% reduction in total cholesterol at age 40 is associated with a 50% drop in coronary artery disease risk. That benefit shrinks with age but remains meaningful, dropping to about 20% risk reduction for the same cholesterol improvement at age 70. The World Health Organization estimates that elevated cholesterol is responsible for about 2.6 million deaths worldwide each year.
How Doctors Confirm the Diagnosis
When heart muscle cells die, they release a protein called troponin into the bloodstream. A blood test for troponin is the primary tool doctors use to confirm whether a heart attack has occurred. In a healthy person, troponin levels are essentially zero. If your level rises above the 99th percentile of normal values, it indicates heart muscle damage. Because troponin is largely unique to heart cells, an elevated result points specifically to the heart rather than to other muscles in the body.
Troponin levels can start rising within a few hours of a heart attack and remain elevated for days, giving doctors a reliable window to detect the event even if you arrive at the hospital after the initial symptoms have faded. An ECG (the test that measures electrical activity in the heart) provides additional information about which part of the heart is affected and whether the artery is fully or partially blocked.