Heart attacks happen when blood flow to part of the heart muscle gets cut off, usually by a blood clot that forms inside a coronary artery. Without blood flow, heart muscle begins to die. The most common underlying cause is a gradual buildup of fatty deposits, called plaque, inside the artery walls. But plaque buildup alone doesn’t trigger the event. Something has to go wrong with that plaque to set a heart attack in motion.
How Plaque Builds Up in Your Arteries
The process starts years or even decades before a heart attack occurs. Cholesterol particles circulating in your blood can slip into the inner walls of your coronary arteries. Once trapped there, these particles become chemically modified and trigger an inflammatory response. Your immune system sends white blood cells to clean up the cholesterol, but over time those cells become overloaded with fat and die, leaving behind a growing core of fatty debris inside the artery wall.
Meanwhile, muscle cells from deeper layers of the artery migrate inward and produce a fibrous cap over the fatty core, somewhat like a scab forming over a wound. This combination of a fatty core covered by a fibrous shell is an atherosclerotic plaque. Some plaques grow large enough to physically narrow the artery, but many of the most dangerous ones are relatively small. They don’t restrict blood flow day to day, which is why people can have significant plaque buildup without any warning symptoms.
What Actually Triggers the Heart Attack
The critical moment comes when a plaque becomes unstable. Roughly 75% of heart attacks begin with plaque rupture, where the thin fibrous cap covering a fatty core cracks open. This exposes the contents of the plaque directly to the bloodstream. Your body treats the exposed material like an open wound: platelets rush to the site and begin clumping together, and a cascade of clotting proteins activates to weave those platelets into a dense mesh of fibrin. Within minutes, a blood clot can partially or completely block the artery.
The remaining cases are increasingly attributed to plaque erosion, where the surface of the plaque wears away without a dramatic rupture. Contemporary studies using imaging inside the arteries estimate plaque erosion accounts for about 40% of acute coronary events, a much higher figure than older autopsy-based studies suggested. Erosion tends to trigger smaller, less complete blockages, but it can still cause serious damage.
Once a clot blocks a coronary artery, the clock starts immediately. Heart muscle that loses its blood supply begins dying from the innermost layer outward. Research using cardiac MRI shows that after about two hours of total blockage, damage often extends through the full thickness of the heart wall. After three hours, most patients have irreversible, full-thickness tissue death in the affected area. This is why emergency treatment focuses on reopening the artery as fast as possible.
Risk Factors That Speed Up Plaque Growth
Several conditions accelerate the process of plaque formation and make existing plaques more likely to become unstable.
High LDL cholesterol is the primary driver of plaque buildup. LDL particles are the ones that penetrate artery walls and deposit cholesterol. Current guidelines recommend keeping LDL below 70 mg/dL for people at high risk of heart disease and below 55 mg/dL for those who have already had a heart attack or stroke.
High blood pressure damages artery walls, making them more vulnerable to cholesterol infiltration. Stage 1 hypertension starts at 130/80 mmHg, and stage 2 begins at 140/90 mmHg. Years of elevated pressure stiffens arteries and promotes inflammation throughout the cardiovascular system.
Smoking injures the lining of blood vessels, promotes inflammation, makes blood more prone to clotting, and lowers HDL (the protective form of cholesterol). It is one of the strongest modifiable risk factors.
Diabetes damages blood vessels through chronically elevated blood sugar, which accelerates plaque formation. People with diabetes also tend to develop plaque that is more widespread and harder to treat. Diabetes can additionally dull nerve signals from the heart, which is why some people with diabetes experience heart attacks with minimal or no chest pain.
Genetics and Hidden Risk Factors
Family history of heart disease is one of the strongest predictors of heart attack risk, and part of that inherited risk comes from a particle called lipoprotein(a), or Lp(a). Unlike regular LDL cholesterol, Lp(a) levels are almost entirely determined by your genes. High Lp(a) promotes plaque buildup, increases clotting, and fuels inflammation that makes plaques more likely to rupture.
High Lp(a), defined as above 50 mg/dL, is surprisingly common. About a third of people with familial high cholesterol also have elevated Lp(a). The tricky part is that Lp(a) is not included in a standard cholesterol panel. It requires a separate blood test, and many people never get screened. If a close family member has had a heart attack at a young age, asking for an Lp(a) test is a reasonable step.
Heart Attacks Without Major Blockages
Not all heart attacks follow the classic pattern of a large plaque rupturing in a major artery. Between 5% and 15% of heart attacks occur in people whose coronary arteries appear mostly clear on imaging. This is called MINOCA (myocardial infarction with non-obstructive coronary arteries), and it has several possible causes.
Coronary artery spasm is one of the more common. The artery temporarily constricts so tightly, more than 90% closure, that blood flow stops. This can happen spontaneously or in response to drugs and toxins, including cocaine and certain stimulants.
Spontaneous coronary artery dissection (SCAD) occurs when the inner layers of a coronary artery tear apart, and blood collects between the layers. The resulting bulge compresses the artery from within and blocks flow. SCAD occurs overwhelmingly in women, typically between ages 45 and 53, and often in people with few traditional risk factors. It is one of the leading causes of heart attacks in younger women.
Microvascular dysfunction involves the tiny blood vessels deep within the heart muscle rather than the large coronary arteries. These small vessels can spasm or fail to dilate properly, starving patches of heart tissue. Because the large arteries look normal on an angiogram, this type of heart attack can be harder to diagnose.
Blood clots from elsewhere can also travel to the heart. A clot that forms in another part of the body, sometimes related to an irregular heart rhythm like atrial fibrillation, can lodge in a coronary artery or its smaller branches.
How Symptoms Differ by Person
The classic heart attack symptom is a heavy pressure, squeezing, or pain in the center of the chest that lasts more than a few minutes or comes and goes. But many heart attacks don’t look like the textbook description, especially in women, older adults, and people with diabetes.
Women are more likely to experience shortness of breath, nausea, unusual fatigue, and pain that radiates to the back, neck, jaw, shoulder, or stomach rather than the chest. Some women describe upper back pressure that feels like a rope being tightened around them. These symptoms are sometimes dismissed as anxiety or indigestion, which contributes to longer delays in seeking treatment.
People with diabetes may have a “silent” heart attack with little or no pain because nerve damage from diabetes can blunt the heart’s distress signals. In these cases, unexplained shortness of breath, sudden weakness, or lightheadedness may be the only clues. Cold sweats without an obvious cause are another warning sign that applies across all groups.
Why Speed of Treatment Matters
Heart muscle does not regenerate in any meaningful way. Once it dies, it is replaced by scar tissue that cannot contract. The size of the scar determines how much pumping ability the heart permanently loses. Research on patients with complete coronary blockages shows that even within the first 90 minutes, some inner-layer damage is already occurring. The sharpest jump in damage happens around the two-hour mark, when tissue death tends to extend through the full wall of the heart. By three hours, most of the at-risk muscle is gone.
This timeline explains the emergency medicine mantra “time is muscle.” Every minute of delay between symptom onset and artery reopening translates to more permanent heart damage. Recognizing symptoms quickly and calling emergency services immediately is the single most important factor in surviving a heart attack with the least lasting harm.