A heart attack happens when blood flow to part of the heart muscle gets cut off, usually because a blood clot forms inside a coronary artery. The blockage starves heart tissue of oxygen, and within minutes, cells begin to die. But the process that sets the stage for that clot typically builds over decades, starting with slow, silent changes in your artery walls.
How a Heart Attack Actually Happens
The underlying disease behind most heart attacks is atherosclerosis, a gradual buildup of fatty deposits called plaques inside artery walls. This process begins as early as childhood, but it takes decades for plaques to mature into something dangerous. For most of that time, atherosclerosis causes no symptoms at all.
A mature plaque has two parts: a soft, fatty core and a tough fibrous cap holding it in place. As long as that cap stays intact, the plaque may narrow the artery but won’t necessarily cause a heart attack. The danger comes when the cap weakens and tears open. This exposes the fatty core to your bloodstream, and your body treats it like an open wound. Platelets rush to the site, clump together, and form a clot. If that clot grows large enough to block the artery completely, blood flow to a section of heart muscle stops. That’s a heart attack.
What makes a cap rupture? Inflammation plays a central role. Immune cells inside the plaque release enzymes that break down the collagen holding the cap together. At the same time, the fatty core may keep growing, stretching the cap thinner. The combination of a large soft core and a thin, inflamed cap is what cardiologists call a “vulnerable plaque,” and it can rupture without warning, even if it wasn’t severely narrowing the artery beforehand. This is why some heart attacks strike people who had no idea they had heart disease.
Chronic Inflammation and Hidden Risk
Inflammation isn’t just involved at the moment of rupture. It drives every stage of plaque development, from the initial damage to artery walls all the way through to the final clot. Your body’s inflammatory signals recruit immune cells into the artery lining, help form the fatty core, and ultimately weaken the cap that keeps everything contained.
A blood marker called high-sensitivity C-reactive protein (hsCRP) measures this low-grade inflammation. Levels at or above 2 mg/L are considered elevated, and in one registry of young heart attack patients, 60% had hsCRP in that range. What makes this especially important is that inflammation raises heart attack risk even when cholesterol is well controlled. In clinical trials, patients who brought both their LDL cholesterol below 70 mg/dL and their hsCRP below 2 mg/L saw a 65% reduction in vascular events, far more than those who only lowered cholesterol. Inflammation, in other words, is not just a bystander. It’s an independent driver.
The Major Risk Factors
Several well-established conditions accelerate plaque buildup and make rupture more likely. Most heart attacks involve more than one of these working together.
High blood pressure. Sustained high pressure damages the inner lining of your arteries, making it easier for cholesterol to enter the vessel wall and start forming plaques. Hypertension is defined as a confirmed reading of 140/90 mmHg or higher, but risk begins climbing at readings above 120/70. Each 20-point rise in systolic pressure (the top number) significantly increases the chance of dying from coronary heart disease.
High cholesterol. LDL cholesterol is the raw material that builds up inside artery walls. When LDL particles cross into the vessel lining, they get trapped and oxidized, triggering the inflammatory cascade that forms plaques. The combination of high blood pressure and high cholesterol is particularly dangerous. A large study of nearly 74,000 people found that those with systolic blood pressure above 160 and total cholesterol above 220 mg/dL had more than four times the risk of coronary death compared to people with normal levels of both.
Diabetes. People with type 2 diabetes are more likely to develop and die from cardiovascular disease than people without it. Chronically elevated blood sugar damages blood vessel walls, promotes inflammation, and accelerates plaque formation. Insulin resistance also tends to raise triglycerides and lower protective HDL cholesterol, compounding the problem. When diabetes overlaps with high blood pressure or high cholesterol, heart attack risk climbs even further.
Smoking. Chemicals in tobacco smoke damage the endothelium (the inner lining of arteries), increase inflammation, make blood more prone to clotting, and reduce oxygen delivery to tissues. Smoking essentially attacks the cardiovascular system from multiple angles at once.
Genetics and Family History
Some people inherit a significantly higher baseline risk, regardless of lifestyle. One important genetic factor is lipoprotein(a), often written as Lp(a) and pronounced “L-P-little-A.” Lp(a) is a cholesterol-carrying particle whose levels are almost entirely determined by your genes. High levels promote plaque buildup, increase clotting, and fuel inflammation, a triple threat to coronary arteries.
Unlike standard LDL cholesterol, Lp(a) doesn’t respond much to diet or exercise. Most people with elevated Lp(a) have no symptoms until a heart attack or stroke occurs. Your doctor may suspect high Lp(a) if you or close family members have had heart attacks at unusually young ages: before 55 in men or before 65 in women, especially without the usual risk factors like obesity, smoking, or diabetes. Other inherited conditions, like familial hypercholesterolemia (which causes very high LDL from birth), can also lead to early and aggressive coronary artery disease.
Heart Attacks Without Major Blockages
Not all heart attacks follow the classic plaque-rupture script. A condition called MINOCA (myocardial infarction with non-obstructive coronary arteries) accounts for a meaningful share of heart attacks where standard imaging shows no severe blockages. Coronary artery spasm is responsible for more than half of these cases.
In coronary spasm, the muscles in the artery wall clamp down intensely, temporarily choking off blood flow. This can happen in the large surface arteries of the heart or in the tiny vessels of the microcirculation. The spasm is caused by hyperreactive smooth muscle cells that are overly sensitive to calcium signals, leading to sudden, severe constriction. Some patients have both large-vessel and small-vessel spasm at the same time. Triggers can include emotional stress, cold exposure, or stimulant drugs, but episodes sometimes occur at rest with no obvious cause.
Another less common mechanism is spontaneous coronary artery dissection (SCAD), where the inner layers of a coronary artery tear apart and blood collects in the vessel wall, compressing the channel and blocking flow. SCAD predominantly affects women, who make up 81% to 92% of cases. The typical patient is a woman in her 40s or early 50s with few or none of the traditional heart disease risk factors. Diabetes, for instance, is present in fewer than 5% of SCAD patients. Instead, SCAD is linked to underlying vascular abnormalities (found in over 60% of patients when doctors look systematically), connective tissue disorders, and hormonal changes. Up to 18% of SCAD cases in women occur during or after pregnancy, most often in the first week after delivery. Intense physical exertion or emotional stress precedes the event in 12% to 48% of cases.
Acute Triggers That Tip the Balance
Most heart attacks occur on a foundation of years of arterial disease, but a specific event in the hours beforehand can be the final push. In a study of 874 heart attack patients, 46% identified a possible trigger. Emotional stress was the most common, reported by about 25% of all patients. Physical exertion came second at roughly 11%. Less frequent triggers included lack of sleep, sexual activity, caffeine, and cocaine.
Air pollution is another acute trigger most people don’t think about. Exposure to fine particulate matter (PM2.5, the tiny particles from vehicle exhaust, wildfires, and industrial emissions) can raise heart attack risk within just one to two hours. PM2.5 triggers a cascade of rapid physiological changes: blood pressure spikes, blood becomes more prone to clotting, platelets activate, and blood vessels lose their ability to relax normally. These effects are driven partly by the nervous system shifting toward a “fight or flight” state and partly by pollutant particles directly affecting the blood vessel lining. For someone with vulnerable plaques already in place, a spike in air pollution on a given day can be the event that triggers rupture and clot formation.
Why Multiple Factors Matter More Than Any Single One
Heart attacks rarely have a single cause. They result from the collision of long-term arterial damage, ongoing inflammation, and often an acute trigger layered on top. Someone with high blood pressure, elevated cholesterol, and chronic low-grade inflammation has arteries full of vulnerable plaques. Add a morning of intense emotional stress or a day of heavy air pollution, and the risk of one of those plaques rupturing climbs sharply. This layering effect is why reducing even one or two risk factors can cut heart attack risk dramatically, and why people with no obvious risk factors can still be caught off guard by genetic vulnerabilities or coronary spasm that operate through entirely different pathways.